in this situation its very unclear that Kenny is the bad guy

Only because nobody has bothered to even check. Everyone seems to take for granted that he is, though. (Hey, why isn't this horse moving anymore when I beat it?) ;-)

this is Dawn's personal business not hers

That would make sense if canonically, Buffy were less motivated to intervene when people she loved were in danger (not just mortal danger). But I guess we'll just have to accept that that Buffy is dead and gone.