@Kanami-chan
They don't want to lose any groups, accommodating scanlators is one of the primary goals of the site. And whether they could handle it privately or not (there are circumstances where that's infeasible), either way it doesn't mean it's bad for mangadex to come out and say it doesn't support that behavior. At the very least they're just covering their ass, while addressing potential future incidents of more serious harrassment and disincentivizing shitty behavior in general.
The only possible downside is the "they're trying to generate sympathy" angle, but I and others are genuinely sympathetic? Even if it is just a casual "kys" or other sorts of casual harrassment, I still don't think any group deserves that for how they choose to distribute their work regardless of whether I agree with it.
Also it's pretty clear here you have a bias. Like maybe you have legitimate grievance with Jamini's Box or whatever other groups with delays but do you really want to make that stand here? Even if you think the harassers in question weren't a serious concern at least SOME of them were clearly being assholes. Seemingly making excuses for them just comes across as really petty and detracts from your stance. And in combination with the tone used towards pretty much everyone involved, it straight out just seems immature/inappropriate - as much if not moreso than the supposed groups you're accusing.
TLDR
Ultimately there's no downside to Mangadex stating they don't support that sort of behavior, regardless of your opinions on the legitimacy or circumstances behind it. At the very least they're just covering their ass, while addressing potential future incidents of more serious harrassment and disincentivizing shitty behavior in general. You can continue to feel how you want about the groups in question but that doesn't necessitate taking a stance against the announcement itself.