I agree that contacting a person is fine to discuss situations but giving them an ultimatum is sketchy..
Say you include Darkstar, and darkstar included zazarb, but you don't like zazarbs ratings..
You can simply exclude zazarb and not threaten to remove/exclude darkstar unless he removes zazarb, for example..
Or whoever in dt1 included zazarb..
You don't have to go to the DT1 and threaten them to remove zazarb from DT2. Just exclude zazarb yourself and leave them alone..
I really don't consider that a threat or an ultimatum, whichever direction it goes. If someone told me that they'll exclude me as long as I have X, Y, and Z in my list I think I'd say "thank you for letting me know".
I've also explained my exclusions in roughly the same terms to some other users who asked about it. I don't particularly like all this, but the fact is that the vast majority of these discussions ended up revealing misunderstandings of the way the system works (most common being the confusion between trust ratings and trust lists) so I consider it net positive.