TheViceOfReason - this is a basic compatibility issue, as has already been stated many times on this thread.
We're not talking about breaking up an established relationship. 
We're taking about a poster who's having doubts about someone new she's seeing.
That's OK, you know.
This is the time for trying someone on for size, as it were. Seeing if you get on, if you like each other, and whether you think you'll be a good fit in the long term.
Something is niggling for the OP, and she's questioning whether things are right.
Your post is pretty much telling her to ignore her own doubts about compatibility - to over-ride those feeling, and to be nice to this person she's only recently started seeing, because being nice to people is more important than gut instinct, and long-term compatibility.
If the OP were discussing her husband, then she'd be getting some very different responses.
You're taking offence where there is really none to be taken. And in fact your advice to essentially ignore her own feelings and be nice to the new chap, is not at all sound.
Believe it or not, it's ok to break up with people - it's especially ok to break up with people before it gets serious, if you think it's not right.