*Edited to add: I think most of the hostility towards MTL is towards the groups that just plug and dump. The ones that don't clean up the translation - no check for clarity or consistency. Few people complain about the ones that do, though, they tend to get a lot of back-handed compliments: "I couldn't tell it was MTL." or "That's pretty good...for MTL."
MTL services weren't as good back in the day as they are now. So, even if a person wanted to put in some effort, the translations might have been wildly inaccurate. They were used a lot less, so the ones doing it typically weren't long-time translator group members. Aside from the low quality snipes, you'd mostly see them with series that had lost the traditional scanlators for a long time, so someone trying their luck with the MTL took over, after many months, even a year or more of inactivity. These people got the most undeserved criticism. They weren't sniping anything and didn't even pretend to be something they were not, they just granted folks without Japanese skills a chance to continue reading a manga, even if the translation might have had some problems.
Now MTL has come a long way, perhaps thanks to the (accursed) AI, plus there are people using it who have the other necessary skills up to the level of any traditional translation group (or individual). I have also seen traditional group members join a project powered by MTL, so the typesetting, editing, etc were quickly fixed.