Wouldn't wish that on my worst enemy

I've never understood people who use the phrase "I wouldn't wish that on my worst enemy". Obviously you're enemies aren't that bad a bunch of people, or the reason that they are your worst enemy is a little flawed. That or you just can't follow a vendetta through.

When it comes down to it, if you're my enemy I wish you so much more than dead. There is literally nothing I wouldn't have done to you for just being a member of that group of anti-me people. The only difference between the standard enemies and my worst enemie(s) are that I'd take so much more pleasure in it.

For me, there's no point in having enemies if you don't want them to suffer. Surely the can be re-classed as lower grade acquaintances or something.