There's an old saying: "If you're not cheating, you're not trying."
It's cynical, yes, but it has a good point: if you're not breaking the rules, you aren't really doing your damndest to win.
But is assuming everyone else is a cheater considered toxic?
A wise man once said:
"just because you're paranoid doesn't mean people aren't out to get you"
Not saying I think so, but I think most would say that people that think good players are cheaters no matter what the circumstances, have a lack of skill and knowledge of the particular game in question. Like you might think someone had no way of knowing you were going throw a skill shot, when really you accidentally showed you were about to. And to actually answer your question, no it's not toxic to assume anything. It is however toxic if you all chat toxic remarks about it, or team chat toxic remarks for that matter.
I once got hit with Caitlyn ult so I called aimbot ( ͡° ͜ʖ ͡°)
