Taking a base and padding your score with cheap kills are 2 different things.
What about...
Padding your score while taking a base?
Padding your score while unscucessfully trying a base?
Who decides if it "really" was a base-grab?
I try to cap a base, but my countrymen suddenly disappear, no more support. Such things happen. Am I now a weak vulcher?. If they had showed up while I was capping and we captured that base - would that have made my vulches suddenly "acceptable"? What if my enemy doesn't believe that it was part of a basegrab? (Because that's how we players think:
We always have a legit reason to vulch,
they, of course, do not.)
The line you are trying to draw is a non-existant one.