Fortunately, Bitcoin is resilient against this type of attack. I can easily make my own fork of Bitcoin, and declare to the world that this is the new Bitcoin. You will just laugh at me, and keep using Bitcoin. It turns out that trying to break up everybodys agreement is like trying to stop a moving train by stepping in front of it. People who do that are deliberately excluding themselves from everybody. Their pretend-Bitcoins just get crushed and left behind, as everybody keeps using Bitcoin.
Well said. The drawback of this (if there is one) is the difficulty by which a cohesive hard fork could ever be achieved. The legacy protocol has become sacrosanct, so changes implemented by hard fork -- like Confidential Transactions or future block size increases -- are likely to lead to permanent network splits. Outside of an existential bug fix, it's becoming more and more difficult to imagine a Bitcoin hard fork where the new network is known as "Bitcoin."
And again, maybe that's a good thing...