75% is generous, normally you need 67% to change constitution laws in most countries. It is always tradeoff how big minority you want give the right to veto majority will. If you think 5% or 10% can veto 90% majoriy, your probably part of this minority and want more power than you actually have.
Is Bitcoin a country; a democracy? You're comparing apples and oranges here. Bitcoin is a consensus driven protocol. Participants that started using it have agreed on a set of rules.
At start, Satoshi choose 32MB as consensus rule, then changed it to 1 MB consensus rule, now it can be changed to 2 MB if majority chooses. If you dont want, your free to use 1 MB the same way people were free to choose continue using 32 MB before, none force you anywhere, but you force me to keep using 1 MB. Do you see the difference between dictatorship verus libertatian here ?