I think it was less offense and more that the term "trap" itself carries a fair bit of baggage. Especially considering its origins as straight guy "bait". It is by its nature devaluing. It has nothing to do with what you enjoy (crossdressing), but rather the (insidious) relation of what you enjoy has to do with straight men (trick them into finding you hot only to reveal you are a guy). I think that is what Terminal was going for when they were talking about self-respect (and I would ask that they forgive me if I got it wrong.)
See, there's a critical lack of understanding here.
The butt of the joke is not the trap, it's the guy. Also, the trap is almost NEVER actually trying to trick anyone, they're just being themselves. It is the guy who projects onto them what he wishes to see.
When there's a joke about a trap, it never demeans the trap, it's always about the guy being dense. If there's any malice at all, it's more on the part of the artist or author who wants to troll their audience (in the cases where they're not just into it themselves and are just having fun) so again, the actual character isn't really scheming or plotting to make people gay because they got a boner at him or anything of the sort.
People are just super duper ignorant here. Hell, I'm not even into this sort of thing and I know this much cause I'm into anime fandom. The ones complaining have to by definition not even be into it either and maybe not into anime at all in the first place and just want to complain about stuff.
There also seems to be no shortage of people who project their insecurities onto what others say about stuff they like.
In general, it's not necessary to qualify these things with "not all anime" each time it's mentioned. Normie acceptance of weebs isn't hung up on r/animemes. "It's normal in Japan" doesn't make it immune to criticism and it doesn't make Japanese culture immune to criticism and it doesn't make the fan interpretation of Japanese culture immune to criticism. Why that last one? Because a huge number fans are on the spectrum and the industry's affinity to pander to every quirky fan out there seriously undermines claims of consuming "culture" instead of a cynical product. There's nothing wrong with liking stuff that's made by fans for fans, but if one needs to get defensive and look for excuses how others supposedly get the wrong idea they are just being pathetic.
But when one tries to criticize a cultural tradition, say, Islamic or African cultures, people are quick to jump at the accusation of phobia-isms and proclaim that it is colonial oppressive thought to try to tell them what's right and what isn't based on our uniquely westerner concepts that stem from whiteness, concepts such as politeness and math.
Why are you trying to colonize Japan?
So, just to be clear, if one person isn't offended, there is no possibility that anyone could be offended?
By the capacity of someone to not be offended, it is proven that the term isn't offensive by itself. It doesn't cause offense automatically as a natural course. It is based on the reciever's point of view and feelings whether offense will be caused or not. Hence, it is their responsibility that they are offended by the term, it is they the ones that need to work on themselves so as to be unaffected by this thing that some others are indeed unaffected by. It is not the work of the strong to weaken themselves so that they can understand the weaklings, it is their responsibility to strengthen themselves, so that their being will be similarly unaffected by these terms.
If you wanna ask why, the simple response is that people will be happier that way than in the reverse way. Yes, even when some people fail to strengthen themselves. The ones that do succeed will still amount to greater happiness than if you just stifle the ones who are already strong and don't push the weak to improve, because the world will NEVER be one which doesn't require spiritual and mental fortitude to be happy in.