> Couldn't assumevalid fail if the majority of hashrate built on an invalid block for long enough that everyone who knew it was invalid gave up and left and then those who remained set a new `assumevalid block at a higher height?

Then any user running a full validation with `assumevalid` disabled or set to a lower block than the offending would reject the best chain. Hopefully one of them would raise an alarm. Also, if a block had been invalid and people got forked off, how would the grand conspiracy have kept thousands of naturally suspicious and widely distributed Bitcoiners from getting that message out?

Couldn't `assumevalid` fail if the majority of hashrate built on an invalid block for long enough that everyone who knew it was invalid gave up and left and then those who remained set a new `assumevalid block at a higher height?

I realize this is starting to sound a little ridiculous, but I'm trying to figure out where the downside is. 

It almost sounds too good to be true that nodes can safely skip validating script before an assumed valid block. Just like pruning can be really awesome, but comes at the cost of needing to resync if the node trues to load a new wallet. 

I'm curious what the price that an `assumevalid` node pays for the benefit.

Scoresby

Every block was the chaintip when it was freshly mined. For the 

 assumption to fail, you must assume that the entire network accepted an invalid transaction in a new block without anyone noticing that mistake, or someone switched out parts of the blockchain in everyone’s copies of the blockchain without anyone noticing. I guess, yeah, that’s the assumption that there is at least "one honest node that would have raised alarm", and you always have the option to be that node yourself by turning off assumevalid.

bitcoin

bitcoin_beginners

Are we all running SPV nodes?

Every block was the chaintip when it was freshly mined. For the `assumevalid` assumption to fail, you must assume that the entire network accepted an invalid transaction in a new block without anyone noticing that mistake, or someone switched out parts of the blockchain in everyone’s copies of the blockchain without anyone noticing. I guess, yeah, that’s the assumption that there is at least "one honest node that would have raised alarm", and you always have the option to be that node yourself by turning off assumevalid.