Could it be partly because they can't defend themselves, and partly because when we ourselves die we would prefer people to remember our good sides rather than our bad sides?

I think it has something to do with the fact that the dead aren’t available to counter your negative argument/comment about them!

I don't see any reason not to express your true feelings about a public figure. When it comes to friends, family and acquaintances, I think we need to hold our tongues in deference to their loved ones.

If they were shit human beings in life, their being dead isn't going to magically change that.

YES! This double standard actually REALLY pisses me off..

There was a kid at my highschool who was a DICK. I had a friend, who was openly gay, and this kid would give him so much shit. He was one of the popular jock kids and I will never forget the terrible remarks he would say to us everyday.

Well apparently a few years after highschool, this kid died behind the wheel due to drinking and driving. Lots of old highschool friends on facebook were "mourning" him and "remembering" him but I had nothing good to say about him. I said good riddance. and people got mad at me! Even after I explained myself and why I felt that way, apparently I am supposed to magically forget how horrible he treated my friend, etc etc. UM NO. Fuck you and fuck that kid.

Sorry... I have come across this quite a few times in my life... that was just one example...

If I am a dick, and I die, please feel free to spit/piss/curse on my grave. It won't matter because I will be dead.

I don't believe it matters when you "disrespect" the dead.

We just lost one of “ours” to suicide. The lady was a dear friend of my sister, but I personally didn’t care for her at all. I never saw anything particularly worthy about her as a human being- but my sister loved her.
Now here I am trying to console my sister for her loss without mentioning what a pos this woman was.
Not an easy conversation.

All of the Bushes should be tried for treason and hanged

The living can, theoretically, defend themselves against slights to their character. The dead cannot.

Say whatever you want - the dead won't care. Neither will most of the living ...

Who's expecting that from you?

Unless it's someone who is generally agreed to be evil, like Hitler or Bin Laden, there is no civilized reason to speak ill of the dead upon their passing. There will always be time for that later.