I can't speak for everyone else against this change, but for me, my main beef is where this is going and pretending you are adding something that is in line with the original purpose of EPCOT Center, when it obviously is not.
I don't have anything against GotG, in fact, I am a huge fan of the MCU and would have been ecstatic if this was going in RNRC. I was earnestly refreshing the Live Action panel today just for a snippet of Infinity War news.
The dislike towards this is mainly fueled by the fact that recent IP insertions into EPCOT have been lackluster. It's not in line with what EPCOT is about, which is why people on here are so upset.
I'm not in denial that this isn't happening. It is, for better or worse. But, like you said, I can dislike this news. I can post negatively about this news. That's the purpose of a discussion board like this one. For the record, I'm 17 years old. A target demographic. So I'm not pining for the good old days, because I never lived them. But I want to. I want to ride Horizons and get the sense of awe that everyone talks about. I want to ride the original Journey Into Imagination and feel like anything is possible. But I can't, and probably never will. I hope this ride will be good. I was very happy with the rest of the announcements today at D23, for the most part.
I just want to experience EPCOT Center one day, that's all.