I think it really depends on the context, though I agree that there are some users on here who will downvote any contrary opinion that comes their way. Expressing appreciation for League and Riot independently, including on matters others disagree with, is obviously fine, and could be done more often (there's a lot to like in League, and the game can be a lot of fun). The problem, I think, comes when said appreciation of League is weaponized and directly used against someone making a complaint. "I personally like League" is very different from "I personally like League, therefore any criticism you make of it is invalid", and the latter unfortunately does crop up on threads from time to time. Your very comment here kind of sets itself up to be downvoted by a) directly answering a complaint thread, and b) doing so without actually addressing the thread, but by drawing attention to yourself and how you're being silenced (you're not).
Your one other comment drew downvotes because it accused various people of circlejerking, when their complaints were directly based off of Riot's own design philosophy, namely design points they have put forth, without explaining why their opinion changed once they started releasing game updates that went against them. You weren't saying anything positive about the game, you just attacked a bunch of people out of the blue without really making any kind of solid case of your own. This itself I think has been a recurring problem with a lot of users who claim to be positive on here, because in reality many of them in practice just get on a high horse and try to make people feel bad for expressing their own opinion, which as you can imagine is rather ironic in this context. I welcome positive appreciation for League, and more nuanced and measured opinions in general, but just like criticism, this appreciation shouldn't be expressed at the expense of people who like League differently, nor does it need to be followed by feigned persecution if used as a weapon against others on this space.
