>bakedfish or horriblesubs
Those aren't subbers. They're barely even groups, *fish is low-quality re-encodes for shit computers/other devices, and horriblesubs is a script that releases streamrips. *fish will vary in what sources they re-encode from, but horriblesubs (as well as erai-raws, and some others) will be from whatever the stream source is, usually crunchyroll for most seasonal simulcasts these days, but also provisionally sentai (hidive), amazon, netflix, etc.
So the real problem is that the competence and views of the person actually doing the subs for each show varies wildly (even within one stream source) and is largely obscured by all being under the same label. This is made worse by most subsequent releases of the same show by fansubbers just using a revised and re-typeset version of the original sub, rarely will you see an entirely new original translation for an episode of something that was originally simulcast. Fansub groups may or may not make the script better, though.
So, as far as someone injecting bullshit into the subs goes, you won't know what you get until you get it. But the primary benefit of watching subbed anime is the original lines are still there alongside, so it's always possible to detect. Anime watchers still have it better than manga readers in that regard.
tl;dr, it's not called horriblesubs for nothing.