The magnitude of an action may change not only the strength of its impact, but the direction. If you became a dentist, for example, you would certainly be an asset to our society. But what if everyone became a dentist? Who would bake the bread? Who would build the houses?
It is a lot easier to prove that you don't love someone than it is to prove that you do, but one of the best 'proofs' I know is the desire to devote time to the person with no expectation of any sort of compensation, including gratitude, in return.