One of the primary value propositions of bitcoin is censorship resistance.  If it loses this feature, people will lose confidence and the network will suffer.

75% of the hash-rate can disregard the other 25% and build on their own blocks.

Are you suggesting the current state of mining centralization is fine? No issue? 

 Censorship resistance is a dynamic, anti-fragile process, not a static feature. If there is censorship, people will pay higher fees to overcome it.