Smashboards

I don't know for sure, but I'd guess when they appeared in Melee, since nearly everyone who wasn't known at launch was a clone (Dr. Mario, Pichu, Roy, Ganon)

They became far less hated in Ultimate once they were called echo fighters, though.

I figured it started in Melee too, I never hated Clones to begin with, and I think every smash game should have them, but they have to have way more unique characters first.

What is your stance in them?

Never really had an opinion before Ultimate. But once they were called echo fighters, I think there should have been more of them (in moderation, of course). They were always meant to be ways of making additions without taking up too much time. They should have had some for bonus DLC instead of certain Mii Outfits or maybe even free with the fighter they're based on (so you can't cheat a DLC character by getting their echo). Shame, because I think some echo picks (like Daisy and Chrom) were some of the best in Ultimate and there are some characters like Octoling just begging for an echo.