You're soo close to seeing how harmful ideology can radicalize vulnerable people into terrible acts. I'm not going to attack your beliefs, nor William's. All I'll do is point out there are thousands of games, hundreds of thousands, many with forums and much larger communities.
Take a moment for self-reflection. Perhaps the reason hate-speech exists as a concept is because some people literally can't take the joke and terrible things can happen. Obviously that doesn't make you or anyone else in the blockland forum responsible for the behavior of a murderer.
Like you've said, blockland is an echo chamber. It's not a coincidence that he was a large member of this community. You'll notice I'm not taking a political stance. That is because a) my political beliefs are well aligned with partisan politics and b) the political stance doesn't actually matter. It would be no different if you were a communist and sephiroth was a trans person who shot up a school (a thing that happened in my city, actually)
Both you and he gobble up the same flavors of propaganda, so it's no surprise people lump y'all together. We all eat propaganda at some point, but it's rare I get to see effects described in literature about neo-conservative political violence just directly exhibited.
For example, you say a lot of sensible things. Classic common sense talking points. It's one of the most controversial issues in the US. IIRC, about 80% of anti-trans videos, commercials, and articles (the classic propaganda vectors) are directly funded by oil and coal companies. That's a funny coincidence...
common sense is one of the highest conversion rates to violence from ideology. As a derivative of gay bashing, trans violence is very common, though not very visible as the absolute number of transgender people is like 1% of the population.
I guess my question is: did one of the people you knew and were friends with becoming so radicalized that he committed an act of terrorism change your relationship with your political views or how you express them?