First of all, let me affirm that the whole debate about "reckless act" is a pretext. Even if it is removed in the final version of the law, abortion advocates are still going to oppose it, because they cannot square any law that protects unborn children with their ideology.
The idea that women can be prosecuted for miscarriage if they drink while pregnant is a shocking one. Fortunately, it has no practical application. The critics seem to be confusing two types of proof: proof of mens rea and proof of causation. Whatever standard of mens rea applies, even recklessness, the prosecution still has to prove that the defendant's act caused the death. In most cases, determining the cause of death in a miscarriage is impossible. No prosecutor will be able to show that "the occasional glass of wine" caused the baby to die, especially since most babies in that situation turn out just fine. Compare this to the case which prompted the legislation in the first place: a woman hired someone to beat her until she miscarried, and the state found it had no law under which she could be prosecuted.
Slate makes the point that chemotherapy on a pregnant mother can cause her baby to die, and worries that Utah has "accidentally criminalized cancer treatment." However, women whose babies die in this way can point to self-defense. Such a defense is so obvious--and the defendant so easy to sympathize with--that the state is highly unlikely to prosecute.
But here's the thing: because the bill has been interpreted in the press to include such things, people with no legal background are likely to believe that's the case. If a mother who drank before learning she was pregnant believes that she could face jail for miscarriage, how might she avoid that fate? Easy: by getting a legal abortion. Even if she wants to keep her baby, she might choose abortion if she believes that her only other choice is to wait and see if she becomes a criminal through miscarriage.
For that reason, the governor must send the bill back in order to clarify--in the law, in the press, and in the minds of Utah women--exactly what conduct is being criminalized. Abortion advocates will still hate it, but at least this time around, they'll have to be honest about their reasons.