A significant percentage of the population can be manipulated to support anything, but bitcoin is a consensus system. Hitler did not manipulate 100% of the population to support him. There were many who refused, and who actively acted against him. There was not 100% support for any of the wars in Iraq or Afghanistan. All of those wars had individuals who publicly spoke out against them.
What percentage need to support it? Is a majority of full nodes sufficient?
Even in the
very unlikely case that half the network supported an increase in the money supply, what would happen is that we'd end up with two coins: bitcoin (as is) and inflate-a-coin. No one can force another user to accept inflate-a-coin and I know
many people will continue to support bitcoin. Remember, bitcoin is not a "democracy" and even popular opinion cannot force a change to the protocol.
Viewing coin supply from the environmental lens, there are already cries that bitcoin's inflation consumes too much energy. So increasing the mining reward when the distribution of coins was already efficiently diffused across the population would also be seen as environmentaly-wasteful. To increase the money supply for inflate-a-coin then, I think you'd need to popularize a spin-off from the blockchain that employs proof-of-stake (PoS) consensus rather than proof of work because new bitshares (PoS equivalent to bitcoins) could be issued for no cost and by popular opinion (unlike PoW coins where work is required to create them).