It is obvious from this and similar threads that there are 2 schools of thought on this. Some people are strongly of the view that no-one owns a name and they can call their child what they like no matter who else has the same or a similar name. Others think it is inappropriate for children of 2 people who are close (friends or family) to give children the same or very similar names.
Although the first view is of course technically correct, the fact that quite a lot of people have the second view means that taking this approach could cause fall-out and i think it is reasonable to factor that into the equation, in choosing a name.
Personally, I would not give my child the same name as a sibling or very close friend, or where the name is the name of a child that had died (even if the parents are a bit less close friends or family).
For similar names, or for names the same as children of (say) cousins or slightly less close friends (but who i still see), i would try to work out which camp the parents fall in if possible and decide if it was likely to cause fall out and, if so, whether it is worth the aggro.
Some people of course take it far too far and i would not have truck with that, even if it caused aggro. For example, i would not rule out using a name that someone else had used as a middle name or a name that someone tried to bags years before even thinking of having a child, even if it causes some aggro as i would regard this as unreasonable.
I have seen a couple of examples where it has caused real fallout, for example a work colleague told me his sisters had called their sons the same name and it caused absolutely massive fall out in the family from which they have never recovered. The other is where a man i know gave his daughter by his second wife the female equivalent of his son's name by his first wife (not quite as close as Oliver and Olivia, more on lines of Charles and Charlotte) and the son was really quite hurt and it added to his feelings of being pushed out by his dad's new family.
So I really don't think it is as simple as saying no-one owns a name.