It depends on the blockchain. If you run your own full node in Bitcoin, it doesn't matter what the majority hashrate is doing. If they aren't creating blocks th

It depends on the blockchain. If you run your own full node in Bitcoin, it doesn't matter what the majority hashrate is doing. If they aren't creating blocks that follow your specific rules, you can ignore them. A 51% attack cannot change the block size, for example. The ethereum ecosystem has placed a lot of trust in the ethereum foundation, plus the foundation controls a large percentage of the fully validating nodes, and is in close contact with all major miners, exchanges, etc. For this reason they are much more able to push through contentious changes. This is provably not the case in Bitcoin, as demonstrated by the active segwit vs. hardfork political deadlock.