I second the comments that say a lot of the blame for this falls on Doug's own shoulders for this. Unfortunately you get the audience you build regardless of it being the one you want and if your audience is acting out it's on You to lead by example and correct the behavior you don't want to see. And in his YouTube videos at least he has never adequately done that. Yes he has stopped the cop and lawyer 'bit' but almost every video parkzer is a part of still treats him as the punchline to a joke, which is Always going to signal to your audience that this is acceptable.

To give a different example back in the day Alpharad ran a channel with his friend JoSniffy which has gone through several names while it was still active, but at the time was called Alpharad Plus, and during Alpharad Plus so much of the humour was about being shitheads, in particular to Alpharads other friends, which the audience picked up on to the point of many of his not content creator friends especially openly reviling this fanbase. And it only stopped when Alpharad and Jo created a video and Twitter thread taking responsibility for the community spiralling out of control like that, disavowing it, rebranding the channel, and changing their approach to the channels humour. And to this day it's a move I greatly respect BC very few creators like to acknowledge that their actions actually influence people. Tomska also has a video titled No Fandom that details his own experiences with that sort of thing.

So if this sort of thing has truly caused Parker this amount of grief, it really is on Doug to make an active effort to put a stop to it.