I haven't had time to read this whole thread - but wanted to stick in my 2p's worth. Warning - this may trun out to be long
Firstly basically everyone has the right to choose the name of their children regardless of what others may think - which is probably why many people don't announce names until after the birth - to avoid any comments !
Secondly in the past many people had the same names, and often the same surnames, even in the same village (which makes family history research a nightmare sometimes).
I think it depends on how often you see the people, how much confusion it would cause, and to some extent how common the name is - if you have gone out of your way to choose a rare name then you might have more cause for grievance. If you are adamant that you don't want anyone to use your name you should tell everyone that and get their agreement not to use it first (doubt if that is possible).
My personal experience - I researched my family history, found 5 generations of the same name (very common boys name), liked it, thought I will call my kid that one day. Later got married and coincidentally this name was the only one my DH and I could agree on (no kids on the horizon at this stage - we could come up with loads for girls). We told this story to DH's sister who had 1 child at that stage. She said - yeah - that's a nice name.
About a year later she had another child - called by this name (different surname to us). I was disappointed because I thought we can't use it now, but thought no more of it. Later we discovered that she was well aware of our preference for the name, and given her intense sibling rivalry with DH we assume part of the reason she chose the name was to stop him using it.
We had a child the next year and reluctantly decided against using the name again (because it would upset her). We settled for a name that neither of us particularly liked but neither hated. 18 months later we had twins and had to come up with another 2 boys names (nightmare - we just couldn't agree on boys names). Finally after much discussion we chose a name DH loves and I can
tolerate for one twin, and also a slightly different version to the original name in question (that DH's sister had already used) for the other twin.
A year later we had an email from Dh's sister demanding we change our child's name, because it belonged to her, and her's was the only one in the world (note a very common name). She claims we have stolen her son's identity. If we didn't change it she would start a family feud. They live the other side of the country (we only see them about once a year), different surnames. We told her very politely that we were keeping the name, that it should have no effect on her child's identity. She hasn't spoken to DH since.
A sad situation - hardest of all for Dh's parents who are stuck in the middle.