Your wrong, it is dangerous if just one pool has veto about change thats why 75%, and Gavin asked relevant Bitcoin services whether 28 days is enought time for them to make necessary changes which he received positive responses.
You are wrong. Why not 70%, since a single miner could veto with 26% hashrate? Why not 50% because more miners could veto the change? That could only happen if there was
no consensus obviously.
Its important if just one miner/pool doesnt have veto power. Someone with 26% hashrate cannot veto the change because variance works against him in the long run (check variance in statistic). Thats why we dont need to worry about this as long as some miner/pool doesnt have over 30% of hashing power which is much easier to veto required 75% treshold.
Thank you for your concern one pool with 26% can veto othervise majority consensus for change though.
BTW your avatar which promotes altcoin reminds me why only those who supports Bitcoin are important in this decision
Are you saying that people that support other digital currencies don't support Bitcoin? Actually, the opposite is true.

Altcoin prices are derived directly from Bitcoin's price, making the health and vitality of bitcoin of "extreme interest and concern" to supporters of other digital currencies. It is bitcoin that's opening the door for other currencies. We need the front runner to remain strong and free from subversion.
In addition, individuals involved in altcoins are some of
the most technically knowledgeable and informed in regards to the blocksize issue!
All I saying we can judge whether someone supports Bitcoin in trustless manner mainly by the hashpower they providing, running full nodes is helpfull too but unless the numbers drops a lot not so important as mining.
While there can be altcoiners with best intentions for Bitcoin future, there can be other altcoiners who would like to shift dominant Bitcoin marketshare/useability/popularity in favour of their preffered Altcoin/s. So trustless manner in deciding about Bitcoin support is better which is hashpower.