I'm confused - was the person in the referenced obituary *your* father? And the obituary was written by/for the benefit of his ex-wife and of stepsisters you had no knowledge of/contact with?
If that is the case, then I can appreciate your hurt and frustration.
On the other hand, I can also appreciate their need to lash out - you got only his good side, which would exacerbate their pain, frustration and anger at the way he treated them.
The person who wrote that was rude, yes. I acknowledge their pain and anger, but that obituary does serve as a slap in the face for one who might be truly grieving the loss.
I can understand the need to share that much anger and hate, but I am sorry you had to see it.
Something like that, if it had to be posted on the Internet at all, should really have gone only on a personal, restricted-access page, and it might have been better to just write the words on paper, then burn the letter.
Edited to add: Dotty's comment has me really confused. If the person mentioned in the linked obituary is not your father, then what business is that obituary of yours? If that person is not your father, how are you harmed by the anger and hate there?
Not everybody leaves a positive mark on their wake. Their are many notorious people about whom wretched things could be written on the occasion of their death.
If you choose to read obituaries about other people, who were no part of *your* life, how is what is written there rude to you?
If it was written in the reasonable expectation that no grieving family would read it, then it may have been ill-considered, but to whom is it rude? Random strangers reading?