To think of it as such would be to allow, in this case, a low self-esteemed person to continue to believe that they are giving the gift of themselves to the "one and only" person worthy of it. (Sorry LT. I don't believe relationships are gifts.)

However, I agree with the rest of what LT has said. I will elaborate a bit from my perspective, though.

how do you know if your new sub is mentally ready to submit in a healty manner and if she/he is not, would you go ahead anyways and dominate her/him anyway hoping her self esteem improves somewhere along the way?
You don't know. There's no way to tell. You don't know what experiences have made the person with which you are about to form a relationship. You can get to know them and you can ask them all kinds of questions, but until the collar is on and the contract is signed, you really don't know what the total package of one person is.

Yes, you can dominate someone with low self-esteem. However, when it comes to her self-image and her mental health, the dominant should be very aware of what he is doing.

For instance, many dominants use techniques which would harm an insecure person's image of themselves. Humiliation play, rape play, watersports and scat, depersonalization and many more types of play could severely tear down an insecure person's already tenuous self-image. I have always maintained that it takes a strong, well-adjusted person to submit and I still stick by that assesment.

If a dominant was to enter into a relationship with someone with obvious self-esteem issues, I think it would be in that dominant's best interest to encourage (not order, not commmand and not insist) that the person get some therapy. You don't want to play with a broken toy, so why would you want to dominate a person that might snap at any moment? I'm not talking about violence or anything, but who's to say what triggers episodes with people that are suffering in the self-image department? You don't want to tie up your submissive and be right in the middle of a very powerful rape play scenario and have her break into tears in earnest because she suddenly remembers that the reason for her low self-esteem is because her daddy raped her when she was a child. That sort of thing is permanently damaging to a relationship.

You also cannot tell someone that they need help. You can pass on to them what you observe in their behavior and opine that you might think therapy would be good for them, but you cannot insist that they get the help they probably need. Only the person can decide for themselves that they need help. And the help they need should come from a professional, not a dominant, not a lover, not a partner, not a relative and not a loved one.

The sad thing is that sometimes your partner, after entering into therapy, might realize that this type of relationship is not good for them right now or that a relationship with you specifically might not be good. In that case, the only thing a dominant can do is to let the person go. Selfishness cannot enter into the equation. Yes, it hurts. Yes, it sucks, but sometimes the most important step for someone's well-being is to be on their own for awhile.

An important thing to remember is to try to find a BDSM-friendly couselor. They usually don't advertise that they are fetish friendly in the yellow pages, so you will have to ask.