At least Guy Gardner being gay would be hilarious.
"Any gay character" is not a step up. Especially when it reeks of cowardice. For instance it was so easy for JK Rowling to casually remark that Dumbledore was gay after all the books had been sold. If instead they introduced a new gay character and gave him his own comic that would be taking a chance that it would sell. If instead they introduced a new gay character and put him on the Justice League that might actually have been controversial instead of just being bitched about for a few days.
When you have characters that have been around for decades and have gone through countless character development, who have formed numerous relationships and often cases had spouses and children, what kind of a message does it send to just "switch" them gay? They could have at least found a character without any developed sexual preference like they did with Renee Montoya (who is now the Question and hence gay), but no, they didn't want a character who "comes out", because apparently DC thinks coming out is weak. Still think this is a step up?
you don't need to go back 50 years lol, there were negative reactions when the black spiderman thing went down last year
Ideally Peter Parker having always been white would always be portrayed as white. People bitch when their favorite character's hair color is wrong. What people didn't realize though was that Donald Glover was the best possible candidate for the role in spite of not looking like Peter Parker.
Any given character in media is assumed to be heterosexual until stated otherwise
With most characters it isn't an assumption. Love stories are shoehorned into every medium and when they aren't women are usually only around to flirt with male characters. The "super-progressive" DC turned Starfire into a sociopath who only values humans when having sex with them, and who runs around naked because "she's sexually liberated". It's just another annoying change to stab all your established fans in the back all in the name of finding the elusive new reader. This isn't the old Alan Scott. The old Alan Scott is dead, and by extension so are Jade and Obsidian. Everyone who was pissed off that DC killed Lean Harper a while back, now she just never existed. The list just goes on and on. This is a small addition.