I think incredible care must be made when rewriting the rules like that: The rules _are_ Bitcoin. The stability of Bitcoin's rules _is_ the soundness of the currency. If the rules can be easily rewritten against the will of some users by others according to political whim then what can be trusted? Is the supply fixed? Will coins be confiscated and awarded to others? If that gate is crossed then there is almost always some excuses which is "good enough"-- as was lamented in some of Bitcoin's earliest announcements. And these changes are controversial -- see, for example, the millions of dollars of Bitcoins backing opposition to things like
BIP101 and supporting
core over classic. I don't believe that Core has the power to make changes prohibited by the rules of the system while proposed by an economically significant portion of Bitcoin's users. If it does, by way of inertia or lazyness, have that power I don't believe it has the moral authority: to rewrite the system out from under people risks riding the thin line of theft. And if the system could really be so easily rewritten against controversy: it may bring into question it's ability to uphold any of its properties. This is a dangerous rode that should be avoided whenever possible.
But the only rule that has been challenged is the max block size, and I don't
think there is a strong basis for the claim that it is set in stone as integral part
of the core design.
If changing that relatively late addition places our feet to a slippery slope
where anything can be altered on a whim, that is equivalent to saying that
the user community is just plain stupid, and perhaps deserves to be parted from
its money. I find it hard to believe that a proposal to change something that had
been the part of parcel of Bitcoin right form the genesis (like supply curve or
PoW algo) would be successful in the long run, and I think the "economic majority"
knows that too.