The problem with casual gamers is not the gamers themselves, but when the industry starts designing games primarily for casual gamers, making the game so friendly to half hearted, occasional play, that it becomes a joke for someone who wants an experience worthy of the "hardcore" investment of time and effort. Simply adding higher difficulty levels to a game which has been inherently simplified for casuals is not the same thing as making a genuinely deep, and hardcore experience... especially seeing as difficulty has less to do with a game being "hardcore" than many might think, in many cases it's the depth of options (and not hidden depth) and/or the simple scope of a gaming experience intended to take hundreds of hours, rather than something a casual can complete in half a dozen hour long game sessions.
In theory both kinds of gamers should be able to co-exist, as long as enough titles are produced to keep both groups happy. The problem is that as the casual gamers outnumber the real gamers, and are also substantially less demanding in terms of quality, innovation, writing, etc... the gaming industry chooses to release titles almost exclusively designed for casual play. Something which has gone so far as to see ongoing series of games gradually dumbed down and simplified so as to be more approachable to casual gamers. An example of this would be how the available options in the "Elder Scrolls" series has gone down with each installment, or how despite massive demand which has been able to carry some indie companies, we haven't seen much in the way of AAA level RPG releases with turn based combat, full party creation, etc... It's all "simple, streamlined, real time". In general the hardest core gamers the industry caters to are the so called "Gun Bros" and really they are a form of casual gamer, with formulaic shooter games replacing clickfests like Farmville and the like.
To be honest the criticisms never really went away, it's just that the gaming media has spent a lot less time being critical of casual gamers for a long time, the message being one of acceptance or surrender from that direction for a while. Not to mention the tendency of some forum moderators in various sites (not really here though) being fairly militant in going after people who are anti-casual and express strong sentiment in that direction. Honestly though the biggest transition is simply that the whole casual gamer thing has seen most of it's energy directed at the gaming industry for catering to casuals to the extent they do, rather than at the casual gamers themselves, which is how I mostly approach the subject. I do not generally care how someone plays a game or what they enjoy, as long as I can find a steady supply of the kind of games I want, produced at an adequate level. Indie games are fine, but I myself want the bells, whistles, graphics, and other innovations attached to serious titles, as opposed to entirely being invested on casuals. Right now my choices largely seem to be indie games with a lot of depth that look like something my cat might have coughed up, or relatively high quality experiences that are also extremely shallow so as to draw in the casual market. Exceptions exist, but are very, very few. Also a big part of it is to produce enough games to keep the relative markets happy, simply put, even considering indie development, there just aren't enough games of the desired types to keep the hardcore gamers sated as they play them. Sure a hardcore gamer might put hundreds of hours into a worthy title, but when he's done, he wants to move onto another game, and it breeds anger when there aren't any, and even more anger when they are taking a much loved series and hyping how casual they are now making it.
Ideally, it should be a simple matter of "you play your games, I play mine" but the gaming industry just isn't willing to do that. The industry has increasingly been taking the role of villain here, but there is still a lot behind the basic idea that if casual gamers can be forced out one way or another, the gaming industry will produce for it's remaining consumers. Something which has increasingly become less and less likely with the gaming media being friendly towards casuals, as opposed to siding with the hardcore gamers in trying to force them out, into other hobbies. In general you'll see tons of articles like this defending casuals on gaming sites, but very few people vilifying them, not to mention I can't remember the last time I saw someone chased off of major gaming sites for being too casual. None of which is a bad thing of course.