Consensus? What does that mean? Hashpower? Non-mining nodes? Wallets? Percentage of BTC in existence (hodlers)? What arbitrary number would you like, if 75% is too low?
That means everyone. Miners, services, users, etc. You can't do this quickly and you can't do this with 75%. Essentially in order for a hard fork to be an upgrade the threshold has to be so high that the old chain has no chance of living else you're splitting the network in two. I'd say 95% being a minimum. Also, anyone arguing that a single entity could prevent the hard fork because of the threshold, the same can be said with 75% with just a small group being against it.
...
Ignoring, for the time being, that there are no Bitcoin game mechanic for BTC hodlers to make their opinions known (vote).
...and that thousands of non-mining nodes can be created on a whim, at a minimal cost:
Your 95% "yes" demand (other than being arbitrary and virtually impossible to reach) pretty much guarantees equally bitter, draconian contraposition (the scope of which, I hope, you're starting to appreciate).
5% can't stand in the way of 95% for long, not without millennia of history and standing armies at your beck and call.
You've turned into the very despots Bitcoin was meant to make irrelevant.
Nice going.