Good for Cameron. Abortion for whatever reason is a matter for the woman concerned and her doctors, and her family where she feels that's appropriate. It's not a matter for the Daily Mail to decide, or pro-lifers, or pro-choice for that matter - that individual decision is one for the individual to make, not for anyone else to second-guess.
Once you start fiddling around and imposing conditions, you'd create real cruelty. Because who chooses which illnesses and disabilities are severe enough to justify an abortion? Me, you, Anne Widdecombe? It's not an easy 'condition X is OK and condition Y is not' equation. You can't necessarily predict in advance how severely a baby will be affected.
That does not mean anyone values the lives of people with disabilities any the less. Because they are real people who exist, just like the rest of us. For me, and for the law as it stands, there is a huge cut-off point at birth - a live baby is a human being with rights, a fetus is a potential baby that is part of an adult human being who has the absolute right to decide what happens to her body.
FWIW I have a medical condition myself, and could easily have been aborted for social reasons (my parents weren't married which was still a big deal back then). Doesn't bother me in the slightest. Or make me inclined to restrict the rights of anyone else in my mother's situation.