For one thing, the dead are no longer there to defend themselves, so its rather a cheap shot to wait until they're gone to criticize them. That's why its considered a classless move to speak ill of the dead, especially right after they're gone. It also shows a level of dislike coming close to hate to immediately express joy at someone's demise, and that's also something that speaks more about the person expressing the glee than about the deceased it is being made towards.

Making an evaluation of someone's legacy should wait until there's enough historic distance to make an impartial judgment, and a couple days or weeks isn't nearly enough time. For example, I don't think Buckley's "dining with Satan" for being a conservative, as a couple of the commenters put it. I make an exception for proven crimes against humanity (massacrers, for example), but Buckley didn't commit any. He had his weaknesses, but who among us is without flaw?

If you do consider conservatives to be "philosophers of tyranny," I'm off the boat with you at that point, though. Conservatism <> fascism, just as liberalism <> communism.