Some of the reasons are set out in the dissenting opinion in National Federation of Independent Business v. Sebelius. Unfortunately, the Constitution says whatever 5 out of 9 Supreme Court Justices say it says so, at least for the time being, the majority opinion controls.
Round two will be whether the forced funding of abortion violates the free exercise of religion.
"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof, ..."
Ayn Rand writes ...
"One may argue about the later stages of a pregnancy, but the essential issue concerns only the first three months. To equate a potential with an actual is vicious; to advocate the sacrifice of the latter to the former is unspeakable."