Perhaps, but that's besides thepoint, heroes becomming villains are almost universally unpopular. If Stark had killed Cap in CW, fan boys would have screamed blue murder. Since CW isn't a conventional war, Tony can't use the excuse that battle field conditions as a reason to allow him to kill Cap, it wasn't a kill or be killed situation. Besides Tony had a million non lethal ways to take out Cap and Stark killing Cap would have forced and very OCC.
Yeah you are right but they can just ignore them and keep going. I am what people might call a "Venom Fanboy" and I'm not the only one out there but they have kept that horrible Scopion-Venom which I know a lot of Venom fans hated. Why not this?
As for the civil war killing. Here is how I see it could have gone. That big fight with all heroes vs heroes Tony gets caught up in it and beats Cap up too much or knocks him on to something that sticks through his chest impaling and killing him.
To Tony he would be justified as it was for the cause and also he just lost his head in the battle it's natural he is human. To every other hero he is the guy that killed an icon. To villains he is one of them now.
Slowly he starts drinking again maybe even takes drugs. Slowly he realises what he did was wrong but that time it is too late. He has since beat Spider-man , the avengers , punisher and more and is wanted by the police for murder.
Eventually he is a desperate man with no where to go. It's not OOC just a new character development hell he ****ed up Spider-man's life and pretty much said he knew it would but he was going to anyway making him unmask on tv.
And like they say desperate men do desperate things. He has lost it all , his friends , his reputation , his money. He starts to think "ok maybe I'll rob this bank , hell the amount of times I've saved the city i think they owe me"
and eventually you have it. A villain created with the longest back story ever.
but like I said you don't agree which is cool so I agree to disagree on this one