Many societies used to use such practices. Didn't Ancient Greece used to do so with anyone who was physically deformed as well?
That wasn't abortions, as they obviously couldn't know in advance if the child was deformed. However, it's being said that the Spartans killed newborn babies that didn't reach certain physical standards. It's important to remember that in many ancient societies, mentally challenged children/people were often revered as being "touched by the gods," so killing them was not a norm way back yonder.
I've had this debate a hundred times, and it's never going to go away and will always be exploited by elitist hate-mongerers of all kinds. It's such an easy question to ask: "Why shouldn't a blind, deaf, deformed and possibly mentally challenged crack baby born with a lethal addiction be aborted?" And then we're off again.
@DW: Yes, I don't think that there's any doubt about strongly liberal societies being breeding grounds for hate groups. I actually have a pretty good example: Back in the late 80s and early 90s, Norway's laws on abortion was a complete free-for-all. This lead to young girls using abortion instead of birth control, the consensus being "Who cares if I get pregnant, I'll just get an abortion." This in turn lead to the emergence and popularity of an extreme group of militant anti-abortionists, unlike anything we'd seen or heard of before. They never got as far as in the US, meaning they didn't bomb clinics or kill doctors, but they were certainly getting there. As is usual in this country, people were slow to react. When finally the Ministry Of Health sounded the alarm, it was not uncommon for young girls in certain parts of the country to have had 3-4 abortions before the age of 20, and the anti-abortionists were organizing violent demonstrations, tossing burning dolls at clinics and mailing stolen dead foetuses(sp?) to the Prime Minister.
What happened was basically that we got stricter laws on the use of abortion, but also lowered the legal age for getting birth control for women, and made birth control pills (almost) free. The result was almost instant, as the number of registered abortions dropped by a whopping 55% in a year, and the rabid anti-abortionists were confined to the "nutcase-extremists" -closet, and has practically never been heard from again.