Well the Bitcoin code can be changed, but it's kinda hard to do because 51% of the network has to agree with these changes. But, I see your point and I totally agree with you. You don't like it? Who the hell cares, bye.
No.
Even if 51% of the network agrees with a major change then it does not affect Bitcoin. What happens is that the 49% that does not agree with the change is still Bitcoin and the 51% that wants the change becomes a new coin
by design.
Even if you get 75% to agree (with a major change that causes a hard fork) you still have 25% of the "die hard" miners and clients supporting Bitcoin and the 75% have just created a new alt coin.
I would argue (semantically) based on nothing but my opinion, that a chain with greater then 51% of the network agreeing to would continue on as **the** bitcoin (chain), and the 49% left behind without the changes woudl have to be then considered to be the alt-coin.
Surely the larger % (if greater than 50%) must be considered the "main chain". If i were to boot up a pre-hard-fork bitcoin instance now under you logic that might be the only node in the world running *pure* bitcoin, with the 99.99% of us on the current chain simply using an "alt-coin".
Your point largely still stands though...