Why cant you burn a military draft card?
Qualify the question a bit and I will be happy to answer. Do you mean why is it illegal to burn a draft card or why is it (or is it) socially unacceptable/morally wrong to burn a draft card? The fact is that you can burn a draft card but it is illegal. For a legal discussion see US v. O’Brien. I think there is a good wiki entry on it.