If someone doesn't want honesty they shouldn't seek opinions. This board would be totally pointless if we all just said 'gorgeous name hun' (I hate the term hun by the way, just pointing out that this is definitely not a 'hugs huni' board.
For me it depends how the post is worded:-
Which middle name? - I don't comment on the first name choice, it's clearly chosen and an opinion on it isn't being sought.
Which one do you prefer? OP requires honesty to make an informed decision. If I like all bar one or two, I will mention my dislike as they may find it useful, especially if many posters feel the same about the same name(s). I'll balance it out will positive comments on the name(s) I love. If I dislike them all, I will just tell them which one I dislike the least, being careful how I word it. I'm not going to pretend I love a name if I don't but I'll probably say "none are really to my taste but life would be boring if we all like the same thing. Out of those I would pick _".
Do you like _? Well they're clearly asking for opinions. It's hardly going to be helpful if the only responses are "yes it's lovely." If 90% of posters say "I really don't like that because..." it's either a) going to make them rule it out (probably for the best if it's that widely unpopular) or b) decide they love it so much that even other people's negative feedback doesn't put them off. Win win. Either way they'll discover how much they actually love it, whether they can see past other people's opinions or not.
Depending on the name(s), the latter two questions usually get a mix of responses to balance it out anyway.
You have to have a thick skin to post on a names board. Many people don't wish to discuss with friends and family before the birth, and those who do can't necessarily trust loved ones to be honest. Better to seek that advice from strangers. As long as posters go into it in the knowledge that no name will be universally liked it's fine.
I definitely agree there are ways of saying things and there's no need to be out and out rude but an honest "I don't like it because..." is perfectly acceptable on a board like this. Surely that's the whole purpose of this place?