> If a big crypto-community notices an attack, the cost of a 51% attack would rise
Would it though, really? Why?
On the contrary, someone performing a 51% attack can and will freeze out all other miners, leaving them operating at a pure loss. If the attacker manages to keep up the attack, he will be able to bankrupt the competing miners, forcing them to turn off their hash power, and thus lowering the cost for himself.
The number of transactions that can be altered from a sustained 51% attack would be so few and recent (last 10 minutes) in comparison to cost that it makes it not worth it
Would it though, really? Why?
On the contrary, someone performing a 51% attack can and will freeze out all other miners, leaving them operating at a pure loss. If the attacker manages to keep up the attack, he will be able to bankrupt the competing miners, forcing them to turn off their hash power, and thus lowering the cost for himself.