Plan B and the assumption of reduced implantation.

There's a random assumption that Plan B causes reduced implantation even though this effect has never been shown. As such the conclusion is that it causes abortion and thus is murder! However, beyond having no evidence, there's a reasonable idea that it might be less than just non-existent. The reverse might be true.

Progestational drugs, including levonorgestrel, are used therapeutically in assisted reproduction because they increase the rate of successful implantation and pregnancy.13 That observation a priori reduces the likelihood that Plan B interferes with implantation; it even raises the counterintuitive but undocumented possibility that Plan B used after ovulation might actually prevent the loss of at least some of the 40% of fertilized ova that ordinarily fail spontaneously to implant or to survive after implantation.

JAMA - Plan B and the politics of doubt