A number of people seem to have been focusing on the first half of your title.
If a game is meant to cater more to self expression and choice instead of raw performance, the thought of having something limit on that is unthinkable, but what if we took the idea of a cheap tactic to an extreme? Sure, one might hate how iron sights have "ruined" modern shooters, but is anyone going to take them seriously when they complain about how they can't hit people while running around and never aiming properly? No. It's an explicit part of the game. You shouldn't complain when fighter caters to people who used more than just basic attacks or when a strategy game rewards people for using the "cheap" tactic of using synergistic unit combinations. However, people seem to lose their shit the second that someone does something unexpected or not having an instantly obvious counter. Some games might have this as an inherently limiting factor, but games that are played competitively simply would not work if there was an undefeatable tactic.
Case and point: Counter-Strike. I suppose Star Craft or Dota and it's assorted clones might be better examples, but my knowledge of tactics and strategy with counter strike is a bit more intimate, so bear with me.
I don't think I should have to justify Counter-Strike as a competitively viable game when it's been played for more than a decade with new tactics still emerging. With thousands of dollars on the line and thousands of teams playing in the various leagues, the fact that a handful of different teams are constantly coming out on top should be proof enough that the winning is not a matter of chance. How can this be possible with cheap weapons like the AWP, the machine gun, the auto sniper, and the p90? Simple, they aren't the end all be all of playing counter strike.
The reason the spray heavy guns seem cheap is because they allow players to kill enemies very quickly without as much effort as certain other guns. However, you'll notice that the p90 and the machine gun are practically never used in high level league matches. The reason is because a perfect or near perfect performance with such a weapon will never be as good as a perfect performance with the more competitively viable assault rifles.
Against an armored opponent, both the p90 and machine gun will do less than the damage required to kill a fully healthy player with a head shot and it takes just as many bullets to kill someone spraying a p90 or machine gun as an m4. The reason a p90 or a Machinegun give an inexperienced player an advantage over a person with an assault rifle is the far more forgiving ammo capacity. A person with a p90 or machine gun has to worry far less than someone with an assault rifle about missing a shot because they have far more shots to miss. This puts them on par with the m4 in ideal situations, but the m4 has far more ideal situations.
The p90 can occasionally get quick kills at intermediate range, but good luck taking on an opponent at long range. Contrast this with the m4, which can score regular head shots at any distance in the hands of a competent user. The machine gun can be about as accurate as an assault rifle if tapped properly, but this makes it theoretically only as good as a much cheaper weapon. In practice, it's still easier to kill an opponent with an assault rifle. Of course, anyone who has been in a pub for more than a few matches is guaranteed to have a story about some idiot who ran around the corner spraying and got a kill with seemingly no effort, but believe it or not, any player can do the exact same thing with an assault rifle. Stopping any automatic weapon rush requires quick reflexes and good shot placement.
Now the AWP is a bit of a special case, because it's still a fairly widely used weapon in the competitive scene. However, even the all mighty AWP is still not as dominant as the M4 or AK47 in competitive matches. This is because it gives the user a very specific advantage in very specific situations, which is that they have a smaller target to aim for when going for a one hit kill. This offers a considerable advantage when coupled with it's near perfect accuracy. The downside is that the weapon requires quite a bit of time to fire off more than one shot and is incredibly hard to use in close quarters. Of course, a good awper can cancel out these draw backs far more easily than someone else can exploit them. As such, facing an awper is still a very big problem.
None the less, good teams and even good players can still kill awpers. The most obvious counter to an awp is another awp. In less equal circumstances, players can learn to peek properly, allowing them to avoid confrontations with awpers at optimal range. Even the best awper will have a hell of a time hitting someone who jump peaks. Teams can also rush the awper. It is probably going to end in a trade kill, but losing an awp is a big financial loss for a team. Grenades can also be used to take out an awper, or coordinated baiting. Correct positioning and angles can greatly increase one's chances against an awper. Lastly, using proper communication will almost always result in the death of a lone awper without support from a team. Believe it or not, few people complain about bad awpers, and I've never heard anyone complain about people scouting, despite the fact that really good awpers often hit people in the head and would be just as effective with a scout in many circumstances. One might even say that a big part of what makes someone good at counter strike is their ability to deal with awpers, either as a member of a team or as an individual player.
Even the all annoying camping isn't even that bad. If a person has played a map long enough, it's fairly easy to tell where people are going to be camping, and most bad campers aren't going to be prepared for someone firing rounds at someone the second they come into view. Aside from that, someone who stays in even the most high traffic area of the map will never do all that well in a game simply because people can go so many other places. Someone who makes effective use of the maps and simply move from good hiding spot to hiding spot while luring in players after them isn't cheap, they simply know how to use the map.
Now, some might have read all of what I just wrote and think "I'm sure plenty of professional players can do fine in such situations, but what about me?" What about you. Yes, countering cheap tactics effectively in any game requires lots of skill, but that's because most cheap tactics specifically exist to cater to people who don't want to get better at the game. Thus, you can either just use such tactics yourself and generally leave the outcome up to chance, or you can use good tactics with the knowledge that you're going to get offed by cheap tactics until you get better. Hell, I still have a kill-death-ratio in source that's slightly lower than one despite the fact that I usually do really well these days simple because I died that many times before I learned how to effectively stop a person rushing around the corner with a p90. However, once you've gotten good, you'll become the bane of anyone who hasn't gotten any better because the tactics they use have a consequentially lower skill ceiling that the ones you use.
This itself might be objected to because some people don't have the time to dedicate to getting super good. If that's that case, they should probably just find a different game. I love left 4 dead or killing because they're games that reward skill, but still allow people who have never even played a video game before to contribute to the team. In a competitively viable game though, every thing you do matters and people are allowed to actually set themselves apart from other players. Getting angry at people for not artificially limiting themselves or for not being able to do just as well as someone who has put in way more time into the game is selling the game short. If it doesn't cater to you, that's fine, you don't have to like it.
In short, are there cheap tactics? Yes. Are there cheap tactics in a fair and competitively viable games? No, and if they're really all that good, you should probably just use them yourself.
