You're taking a fairly strong stance, though it may not seem that way to you. "Same sex marriage was legalized in 1971" is a factual statement not in dispute. "Same sex marriage is a 21st century invention" may seem to you to be the same statement but it carries significant ideological baggage and is a way stronger statement way more in dispute. You go on to say things like "the real reason behind a lot of the LGBT acceptance rates going lower ... is that Muslim migrants have more kids and Islam is a very socially conservative religion." I hardly feel I need to explain why that is not a simple factual statement but really a statement of an ideological and political position.

So while I totally believe you may feel that way, you aren't simply being downvoted for indisputable facts, you've taken a position in a contentious ideological and political debate.