I don't think it's a lesser crime to kill a hobo nobody will miss than to kill a guy with friends and a number of people who know his name.
What makes you think nobody will miss a hobo, that (s)he has no friends and nobody knows their name?
Piss on me for MY values, then say something like that … no words.
Good grief, where the bejesus do you think you saw me say all hobos won't be missed? Some subset of hobos have no friends or anyone who knows them, and I was referring to one from the subset. Other demographics also have members with those features, especially retirees who live alone and have outlived their friends; I don't think it's a lesser crime to kill them either. I specified a hobo only because it's a well-known trope -- psychopaths who want the experience of killing someone are popularly imagined to target hobos because hobos are statistically more likely than the general public not to be missed, so their killers are more likely not to be caught.
I believe the "value" of a fetus or a born person is metaphysical nonsense. I believe in physics, not metaphysics.
Then you should be a fan of the objectively observable fact of biological autonomy, and accept it as a rational point at which to define legal “personhood” to avoid metaphysical nonsense getting involved in legal decisions.

You appear to have jumped from an "is" to a "should". How does that work in your view? From out here, your argument looks exactly as arbitrary as "Then you should be a fan of the objectively observable fact of fetal heartbeat, and accept it as a rational point at which to define legal personhood”.
If we define legal personhood based on biological autonomy, then we'd have to conclude that a guy receiving a direct person-to-person blood transfusion is not legally a person. Does that seem like a sensible legal rule to you?
If it's not a consideration you think should be taken into account, stop raising the issue.
What needs to be taken into account is the specious nature of ”personhood” arguments for restricting access to abortion. Ignoring it doesn’t solve the problem.
If personhood arguments are specious by nature, then "The facts remain: abortion laws kill people and benefit nobody (but lawyers)." is necessarily
a specious argument. Don't make specious arguments. I got involved in this endlessly unresolvable worldview clash in the first place not because restricting access to abortion is important to me but because you were attacking a moderate Democrat with specious arguments, and that serves only to help turn the Democrats into a small-tent party that can't even beat a buffoon like Trump.
I'm also not in the business of deciding what someone's rights are based on how much others value him.
What basis DO you use? You have obviously conferred rights of some sort upon fetuses,
Not at all. I don't confer rights; I recognize them. People have rights, including the right to life, liberty and the pursuit of happiness, because they're endowed by our creator. That our creator happens to be natural selection rather than some religion's fictional character doesn't invalidate that.
but the basis for that is not clear.
True; but that's a huge can of worms, and one more suited to M&P than to PD.