The arguments that the group of telepaths put to Anne are based on the profound difference that exists between themselves and "normal" humans who are not able to communicate telepathically. This above all else would mean that marriage and living with a normal human in such a state of intimacy would be unthinkable. Note what Michael says when he remonstrates with Anne:

You can't, Anne. For your own sake you mustn't... It'd be like tying yourself for life to a cripple.

He therefore uses an analogy to explain how marriage to a non-telepath would be like making a commitment to a disabled individual who was not fully able to do everything that the other person would be able to do. When Anne protests that there are not enough telepaths around for her to ever have a chance of marrying, they try and suggest that they will eventually find others so that she will be able to marry a telepath. However, in the end, these arguments are not enough, and she marries Alan, trying to all intents and purposes to act as if she were just like him.