Wishing anyone a speedy death is fundamentally wrong. I make one exception, and a second, semantic one.
Semantics first: you can wish anyone who is already dead a continuation of their present state. It may not be nice, but this is hate that cannot result in violence.
The more important exception: I wish anyone who has plans to kill people in anger their death. Before they can come into action. I have heard that the Nixon presidency did not much care for lives lost. This might be a reason for people to, at that time, wish people in the Nixon administration a premature death, to counteract more deaths that person might have caused. I therefore wish many terrorists (definitions vary, admittedly) a speedy death. I believe Mr. McCain to be, at heart, a man of peace. Wishing his death is hateful, and is a sign of a weak personality that fears discussion and cannot accept a loss every now and then.
The fact that John McCain was a war hero is irrelevant. That he is basically decent or good is irrelevant. That he is not deeply evil and prone to actual killing is relevant and enough cause to wish the gentleman a long and healthier future.
