Of course it would be wholesome if you could skip even the "Hey, its fantasy" thing, but people are way more on the edge nowdays and the explanation usually aims to avoid some kind of comments i believe.
I don't know with who you hangout with, online and IRL, but you should starts looking for better persons to be with...
It is a trending behavior nowdays and despite you afirming that its uncommon from people who play violent games i strongly disagree since i saw multiple times this same behavior comming from those people. What happens actually is that people who play really gore and violent games tends to hide the fact other than discussing it.
What again is a question of persons (them, not you) and nothing else.
You can just take a look here. Whatever you do and whatever you are, the only topic for which you'll effectively find persons with such behavior is loli/shota. For any other topic, there's the usual couple of Neanderthals and that's all.
Of course, we are expected to all be perverts, and therefore to be aware that we all have at least one behavioral dichotomy. And I insist on the "all" because, as said by
Shelly_seafunk, many have an effective different behavior in life, than the one they have in the bedroom.
But this doesn't mean that only perverts are tolerant person with a functional brain, far from this. It's just that, while being the majority, tolerant persons are, by definition, also mostly silent. They'll not judge you, and therefore you'll not remember that you encountered them ; by opposition to the minority of idiots, who will force you into a totally useless discussion.
Oh, by the way, this is far to be something new. This minority have always existed.
Before internet you had to justify yourself if you listened to rap. And I don't talk about the number of times people who listen to Hard Rock or play RPG, had to explain that they aren't satanists and don't eat children. Before that it was those delinquent Rock'n'Roll listeners who had to explain that, no, they'll not rape your wife and daughter.
And so on... At all time, whatever how far in History you go, there where that bunch of people convinced that only them knew what is good, and who felt the urge to systematically, and loudly, judge, then shame, anyone who wasn't like them ; forcing them to justify themselves or, worse, to hide what they do.
Internet haven't made this happen, nor even it made it worse. It just made it more visible ; yet only when it became something that "everyone access to". And, yes, if you think that it's a majority, then you live in the wrong place or/and hangout with the wrong persons.
Hell, ins't a thing to violent games to have a warning at the start of the game? "Hey, its a game, its fantasy, everyone is 18+ blablabla". People started to do that to while starting some kind of topic, just that.
The finger point the Moon, but you don't even look at it, you directly look at the person who have it...
Said otherwise, you see the consequence, and made it a cause.
There's those warning because, in the early 90's, a bunch of stupid US idiots refused to understand that games effectively are a fantasy. And like at this time already (therefore before they even know that internet exist, and near to two decades before they starts using it) they were already the loud minority, they achieved to freak out enough peoples. And if those persons were able to gain enough visibility, it's because they were standing on the shoulders of all those who said that RPG players were all satanists ; who themselves were standing on the shoulders of all those who said that rockers are all rapists.
In fact, they are the same kind of people than you, just standing on the opposite side. They are convinced that they broke the secret of psychology because they achieved to get 15762 as result for 1 + 1.
But hey brother, i got your point, you just think its BS and revolting having to explain the obvious. I really get it. Still, im trying to reason why this happens, not here to judge if either its right or wrong.
It's funny that you starts by "I got your point", then continue by explaining that you got the point made by the other guy, but totally missed mine.
So, to prevent a totally useless answer:
The reason why this happen is because there's, since the starts of Humanity, and there probably will always be, people who are too full of themselves, while totally failing to see how below the average they stand intellectually speaking. Coupled to another minority who are the opposite, and believe that if they explain the situation, they'll help those idiots.