Controversial Opinion: Only People Killed by Rats, are Angry about Rats
You may not like it, but:
Ratting is a valid way to win.
What people don't want to admit is that ratting often (not always) comes about because of a distinct disadvantage they've been placed in. This can happen because a team spawns a player short, the team had to abandon a teammate that died too deep in enemy area of operation, or any other number of things.
Because I've experienced these (and other) scenarios, I don't get mad at rats. Most often, I am upset that I was outplayed because I couldn't tell where the rat was coming from. When I have teammates who want to play conservative, I understand because they have to prioritize placement over combat because sometimes I have to prioritize placement over combat.
It's not to say that there aren't players who only rat. But especially in ranked, at some point they're gonna need to kill more often to continue to gain RP. And from my (anecdotal) experience, players who default to ratting are far outnumbered by players who have to rat by circumstance.
In a game where positioning is key to winning battles, one should not be upset that they were out-positioned, just as much as one should not be upset when they were out-gunned.
In the immortal words of Ice-T:
"Don't hate the player. Hate the game."