Honestly I think some Americans value personal autonomy to such a degree that it is possible that the fetus = baby argument could possibly convince a few people. One hypothetical scenario could be this: there's two identical twins, and Twin A needs a kidney from Twin B to survive. If, for whatever reason, Twin B refuses to donate one kidney, knowing that Twin A will die, is that tantamount to murder? If the answer is yes, then the fetus = baby argument won't work, but if the answer is no, then the fetus = baby argument could still convince them abortion is morally okay.

Of course, most people don't choose their morality from thought experiments, so I think your point is better anyways