I play minecraft, my friend uses tape and says because it's allowed, it's ok, but I think it's completely unfair to the other players because the perfect grip gives you 10-20cps more
It's unfair because minecraft
In my opinion it's rather unfair but you can see it from both sides.
What I mean by that: of course it's a big game advantage over those who don't use it, but it still takes a bit of skill. If you compare that to e.g. An electric toothbrush or even hacks, that's not a big game advantage, but I wouldn't do it because I would like to win my rounds without any montages that create a game advantage for me.
What's so bad about using grip tape? It is definitely not unfair. If you often have wet hands or have a very slippery mouse, there's nothing wrong with it.
It's not for nothing that you get grip tape with the Logitech G Pro X Superlight, which is made of smooth material. And companies like Lizard-Skins don't exist for free either.
If you think grip tape gives you an edge, buy some yourself. Lizard skins can be purchased inexpensively on CaseKing in many different designs.
For example, I win against my friend without his tape but with tape he has 0 knockback
It has nothing to do with knockback. Just with the feel of the mouse in your hand. Otherwise mice with rubberized sides would be a crime.
You are superior to people without. That's why I don't think modding or cheating is reprehensible because it amounts to the same thing.