It is more than possible that Charles picked Diana for the qualities that he saw in her that would benefit her role as his wife.
We know from Dimbleby why Charles married her - I quoted these parts before. of course you can claim that Charles did not mean the things he wrote into his diary and in letters to friends, that he had in truth much more sinister reasons, but where are the sources for this?
Charles approved a book in which the author stated that Charles was very much intrigued by Diana, that he had an intensity of feelings and that he thought he could come to really love her. He didn't want to listen to warnings by friends who tried to tell him that Diana was more in love with his position than with him. He explained to Diana pre-wedding that Camilla Parker Bowles had been one of his most intimate friends but that "now that he was engaged to be married there was, and there would be, no other woman in his life."
Diana didn't believe him, obviously. Charles' then secretary Michael Colbrone recalled that "it became clear that his employer's fianceé was exceptionally interetsed in the Prince's previous relationships and, in particular, his friendship with Mrs. Parker Bowles."
So for me it is clear that Diana entered her marriage with a clear distrust of the man she was going to marry even though she claimed she loved him. For me, this is not love. IMHO she wanted to become the Princess of Wales and to own the Prince. Sorry, but for me this is the worst nightmare for any man. Because he had been tried and judged for things that happened before Diana was a part of his life. And it's absolutely clear that with tantrums and open distrust you don't get to build a stable, loving and caring relationship.
But you're right: if Charles had been more interested in Diana and Diana's problems, he would never have married her because he would have recognized the potential for utmost damage she brought with her. But he saw Diana as possessing an "easy and open manner, warmth and enthusiasm for rural life", he thought she was "lovable and warm-hearted". To quote Dimbleby: "In the autumn of 1980, the Prince invited Diana Spencer to join a house party at Balmoral. Again she reinforced the initial impression that she had made on his friends. She was so obviously happy and he seemed so attracted to her that his friends warmed to a prospective love match."
But how can she appear in autumn of 1980 at a houseparty to be open and warm when a short time later she started to be mistrusting, started to cry, became eating disorders. Dimbleby: "Having known only the "jolly" girl who had enlivened Balmoral six months earlier, he had been baffled to discover her sudden shifts in mood - her "other side" as he referred to it ( in an interview with Dimbleby.)
That was not Charles' doing, that was a psychological issue she brought with her to the marriage. Sure, the difficult situation in which she found herself had been a trigger, but other girls have managed the transformation from commoner to princess much better and without the help of a background of the nobility and a sister who had been married to a senior courtier. It all went to fast with them and when they realised it, it was too late.
But to blame Charles and him alone is making the things too easy. Diana wasn't the first Royal to suffer from depressions and she could have gotten professional help to find a way to fit in with her situation. But, as someone said: she had "backbone" and was not willing to lie in the bed she had made herself and to work to make this bed more comfortable and acceptable for herself.
And something else: could you please equally willing to name sources for statements like "Camilla handpicked Diana" and to offer sources for quotes which, if they are reliable, really can point to certain character traits but if they are only invented, help nothing on assessing what might have happened in reality. Because this discussion is not about fantasies of beautiful princesses and ugly princes, but about real people who have been part of history.