Legal and Ethical are entirely different. I suggest you look here for legal:
I bet in at least some states it's legal, probably most states.
I believe, at least in reasonably modern vehicles, pretty much all have some form of "auto-disable" feature on the front pax seat. Anything under 75lbs's rings a bell, but now it's owners manual time. I've never seen a state that required manual disables, and wouldn't use it if it did. - There is just too much room for mistake there. Forget to turn it off, or on, or? Which is exactly why the auto systems exist.
Ethical? As in "Should?" There are lots of opinions out there. Here's mine:
1) Risk management is everything. If you ride a motorcycle you know how to drive with exceptional awareness and risk management re; intersections, traffic, and etc.. In my opinion this is the number one consideration. Eg: Put down the cell phone! Use great tires on the car. Disengage idiots and road rage. Those are EXAMPLES, and I'm sure you knew all of it, but the point is we as drivers have so much input into risk management that it utterly trumps car seat choice. And the stuff I see out there suggests this "common sense" ain't so common.
2) How balanced is your risk model? I'm amazed at the folks that strap their kids into a car seat and then insist they shouldn't wear a mask. I'm not gonna get into it, but I find a fair bit of over-zealous focus in one area and incredible irresponsibility in others. Substitute masks for access to guns, locked cabinets, baby gates, smoking, etc if masks and vaccines are trigger words for you. Again, not accusing you, just suggesting balance lacks in some parts of our world and it never hurts to self-check ourselves. In fact I encourage my wife to remind me about caution when I'm moving the kids around lest I get complacent.
3) Would I let a child be in front in a car seat and rear-facing? Yes, if I was confident the airbag (which is a child killer, so be darn certain) was in no way enabled. But it would be last choice. Personally, at three years of age I would go front facing and use a safety vest (like the ridesafer vest) and again be darn certain the airbag was disabled. But this way I've got a better safety factor if it does trigger. It's a bit anal, but I'd take that setup over rear-facing just because if the over-ride failed and the air-bag deployed I'd be afraid it might hurt/kill the child. Just too much energy too close. I see my way as the better compromise. As does my daughter-in-law the pediatrician.
In fact, I'm looking hard at that vest now simply because I've a grandchild and want, in case of unexpected need, the ability to move all three kids in each of my cars. In a few cases the oldest (5) would need to be in front. I'll want him front facing, low and as far back as possible, carefully belted, and protected from belt damage (which is why kids don't use normal belts), and the driver would be expected to drive like a little old lady (do NOT let me wife see this post!)
Luck to you, hope I've helped.
-d