It's not etiquette's place to tell people what to *think*, but it is its place to tell people what to *say*.
Rejoicing in anyone's, even a political figure's, death is not within the realm of socially acceptable conversation. It's talking politics with a capital "P," and worse, can be construed as saying, "And any of you out there that liked his/her policies, I wish the same thing on you!" It's a nuclear option in conversation.
Of course, the opposite is true, and if you're going to cry on someone's shoulder about the death of Politician X, best make sure that that person shares your high opinion. (Yes, I did once have to comfort a distraught friend sobbing about the death of a politician I did not hold in high regard. It's part of the job of friendship.)