If your child respects you then I think "violent toys" are ok.
Let me ty to explain.
If you can tell your child, that's enough now, lets stop and play something quiet.
Or you can tell your child it is not appropriate to shoot the little old lady two doors down
then it's fine, if you child does not have the respect or the understanding then no, I don't think they should yet have "violent toys".
As for video games....
First off if it was a movie, would you let them watch it? Use the same kind of guides, can they spilt fantasy and reality? Can them understand that what is in the game is not appropriate in reality?
And then on top of that i'd limit playing time.
So, I guess part of what I am saying is it depends on your and your child and your combined understanding of appropriate.
I do not think a child taking a toy gun to the supermarket and pretending to shoot customers is appropriate.
I do think a child taking a toy gun out in the back yard and pratising hitting cans is fine - that is development of hand and eye co-ordination.
If it is something your child seems very interested in - channel it with a discipline ie join him in an archery group or fencing. If you have a child who likes fighting join him/her into a martial arts group.
That way they are not denied someting they enjoy but they learn to channel it and respect it.
Does that make sense?