My point is this: it is impossible to draw a bright line, even if one takes the basic "life begins at conception" approach. If life begins at conception, I've had about 18 miscarried children, that I know about. I don't believe that. If life begins at conception, more children are miscarried than are born. If that is true, can one really say that life begins at conception? Life begins at conception, and, more likely than not, ends shortly thereafter? No. You can believe that. I don't.
If life begins at conception, use of an IUD is abortion. If life begins at conception, smoking by the woman, which decreases the quality of the uterine lining and therefore the chance of implantation, could be considered an attempt at abortion.
If you can't draw the line at the moment the sperm fertilizes the egg (and I don't think you can), then you just can't draw a line until viablity, at least. That's my point.
This is only true if conception actually takes place. There are 2 types of IUDs, one is copper and the other progesterone releasing both of these act as spermicides, so IUDs while they do prevent implatation will also prevent conception.