It's not legal problem. Those things are medical ventilators in same manner that bicycle tire pump is a medical ventilator.
Watch the video.
https://www.eevblog.com/forum/projects/ventilator-made-from-car-parts/msg3001626/#msg3001626
And then, probably, you will understand why a real MD will not connect anybody to such contraption.... It is not a real ventilator, it's a Rube Goldberg contraption made by people who don't understand real problem and is equivalent to elementary school science project.
Exactly.
(But yes it is a legal problem too. If some patient dies after being connected to one of those dodgy respirators, the family is very likely to sue. Wouldn't you?)
As I often say, just ask yourself if you'd be OK with some close relative being treated with this.
Now you may keep answering that it would be better than nothing. Which, first, is not necessarily the case as 2N3055 pointed out. But second, there comes the question of whoever gets treated with the real deal and whoever gets the "dodgy" stuff. (Inequalities are already there. Just look at the Boris Johnson case. He was directly put in ICU just in case, whereas the average joe who gets hospitalized in a similar state would just get isolated in a room full of other patients until their symptoms get so bad they need to be transfered to ICU. BJ was not in a life-critical state when he was transfered to ICU AFAIK. And I bet he would get a proper respirator if alternative ones were available. Just a side-thought...)
As to the point of these projects potentially saving more lives than they would kill, we have absolutely ZERO proof of that by nature as they wouldn't get a chance to be properly tested clinically as they should before being deployed.
Now as I said above, I'm all for companies HELPING medical device companies in any sane way they can, under proper supervision. That's a different story. But suddenly improvising, not so much.
Anyway, as many of us have said, there are so many ways people can currently help the world that just improvising medical devices doesn't make much sense IMHO.
This pandemic is putting the whole world on hold and is going to have lasting effects way beyond health problems.