My mum's name is a shortened version of a longer name. She's told me that all her life she's wished she had been given the full name, instead of the shortened name. Some people consider nicknames to be diminutive (indeed some of them definitely are, though others not so much in my opinion). I can understand why Mum feels about her name the way she does, even though her name isn't one anyone would normally consider diminutive or demeaning. I can understand her wish that she had a complete name rather than just the shortening.

My sister is always called by the shortened version of her name. I don't think anyone would call someone who obviously like Alex, Alexander, or who obviously likes Jon, Jonathan, for example. I don't think that's going to be a problem at all.

I think that giving a child a "full" name rather than a shortened name gives them the choice, when they get older, of having more variety in what they are called. And I think that's a good thing. None of my kids will be called such nicknames - they'll all get the full names to give them more options when they are old enough to decide from themselves.