Whether having an abortion tends to drive women crazy, or whether women with a bent to becoming crazy are more likely to have an abortion, isn’t clear from this study. It couldn’t be clear, without controlling for the abortion, which even the U.K. would probably deem unethical (here dear, you are in the group whose unborn baby you don’t want will be killed, where there honey, the study randomizer says we will adopt out the baby you don’t want as soon as it is born).
It's not a chicken and egg argument of which came first. Treat abortion like the Telegraph's headline does. It's a risk factor for mental illness, just like it's a risk factor for breast cancer.
BREAST CANCER RISK FACTORS with references starts on page 25. The importance of reproductive factors in affecting breast cancer risk has been known for a long time. Women who have never given birth (or had a full-term pregnancy) are at a higher risk for breast cancer compared to women who have carried a pregnancy to term.(Page 26)
Think of it like smoking or obesity. They are just risk factors for assorted diagnoses. It doesn't mean any person will get those diagnoses eventually.