I think the answer is simple: You try to get consensus through cooperation and communication,
but if you can't, one side will eventually win by force.
Sure, and if BU, or classic can get 95 % of economic support than this should be not only allowed but encouraged.
As long as its honestly understood-
1) Bitcoin classic is a coup with attempts to remove any influence from many core developers ( Peter R "cooperative" animation is misleading)
2) It is irresponsible and will damage everyone by setting the bar at such a low number as 75%
I understand that technically , all that is needed is 51% , but anyone that decides to fork with 51%- 75% is fundamentally changing the social contract from one that is more anarchistic to one that is more democratic where the majority can coerce and harm the minority.
Many people that I have spoken to make a fundemental misunderstanding that the 95% bar is too high and merely an attempt to stall the project and allow 5-6 % to thwart the efforts of the majority. They fundementally, aren't considering the roots of bitcoin (Cipher-punks , crypto-anarchists ) and how
the social contract is not democratic but far more anarchistic. The reason the bar is set so high is because there are ethical considerations we have to consider when we change the consensus rules.