I didn't say that. It is not possible to prevent against double spending since it doesn't violate any of the protocol rules. You have to quote my entire post to understand what I'm referring to.

Anyhow, I've re-read your posts again and I've understood that your point is that someone can effectively execute a 51% attack if no one else is mining. The probability of anyone executing that is close to zero. One would have to have a significant hashpower before they can even mine a block. Depending on how many blocks ago that is, the cost of such an attack would outweigh the benefits. The effort/resources needed to execute said attack is the same.