What "pill" are we talking about? If you take the "mini pill", which is what Planned Parenthood gives out, that is only a small does of progestin(synthetic progesterone). If you miss one dose, conception is possible but then you could stop implantation. That's why Planned Parenthood gives it out, because they know it will give the girls a false sense of security and they are likely not responsible enough to take it every day.
There is another pill that is a higher does of progestin and usually only taken once a week, which I think still can permit conception but make implantation more difficult.
If you take the pill with both progesitn and estrogen, there is a much higher liklihood that conception will not occur, and there are studies out there that say that compared to a placebo, a women is not more like to have an involuntary abortion. In some studies involutary abortions (stopping implantation) have actually decreased.
I think many agree that the progestin only pills act as an abortificant(sp?) but there is some disagreement over the progestin/estrogen pill.
With these pills you should not have "relations" for a certain amount of time until the drug(s) has had time to affect your body, or else it likely will act as an abortificant.
It is also worthy to note that the "morning after pill" is simply a high dosage of "the pill". It's like if a Dr gives you a prescription for 800mg of ibuprofen pills, you could just take 4 of the OT 200mg ibuprofen pills instead. A woman could just take X number of birth control pills instead of getting a prescription for the "morning after pill" (and there are tables out there that tell women how to do it). It is different from RU-486.
If you believe that unnaturally stopping conception is wrong, then none of this matters.
Something to consider, however, is that there might be other things we ingest that are correlated to a higher rate of involuntary abortion than taking "the pill".
And when does it go from being a "miscarriage" and turn into an"involuntary abortion"? Technically speaking they are both the same thing, but morally speaking we would not say a miscarriage is the same as an abortion.