Tbf most of the people I've been talking with or read discussions of the issue are simply disappointed at how the ratio is skewed to 5(3? Maybe):1 in romatic same-sex supports. There's less anger, more of a confused and overlaying disappointment on the lack of options for those who would want Byleth to end up with another male character but they still love the game anyway.
On the other hand, I have also talked to people who are accepting of how things were handled with the supports… but there were also people who are frankly indifferent to the issue because it doesn't personally affect them; for me, the indifference is the more frustrating aspect since it feels like they're telling me I should just smile and accept we have anything at all. Coming from that end, I can understand why some people are angry and why they would react rather er, harshly, I suppose.
I think sharing an opinion politely and in a level-headed manner goes a long way, forums or otherwise. Hopefully anyone who is planning in contacting Nintendo, IS, etc. with their opinions can share it civilly.