Please accept my apology for causing such confusion. I was supposed to have said that "may I say" instead of "Why I can't say".
Concerning sentences 3 and 4, the reason why they are ungrammatical is that they are not parallel, isn't it?
As I observe, in the first part, the action verb "destroy" is used, but in the other, the verb "be" is used. So, they are not parallel.
To be honest, I don't really know. I am just guessing.