Security on the network depends on the hash rate. If one theoretically had unlimited energy, then it would basically be fiat energy at that point. Part of the security comes from the fact that it would take a great deal of both energy and computing power to attack the network.

If there was theoretically unlimited energy available to bad actors, I'm trying to decide if that would be a problem. If it doesn't cost anything other than [free] computational power to mine blocks, what would that mean for the network?