“It’s not always wrong to attach conditions to a gift. Sometimes the conditions are intrinsic to what’s being given. There’s nothing coercive about a college fund that requires enrollment; tuition support is what the gift consists of. When you give a sibling money for a down payment on a condo, that money had better be put to that use. Nor would it be problematic to tell a relative with an addiction problem that you’ll provide an apartment so long as the person maintains their sobriety. The rationale is that the addict’s choices around substances aren’t fully free. The condition is aimed at protecting autonomy, not constraining it.
“By contrast, your son is fully capable of judging the evidence and deciding what to do with his own body. His choice not to pursue treatment may be misguided, but it’s his to make, and the condition is unrelated to the gift. What your husband is considering isn’t extortion; withholding a benefit isn’t the same as imposing a penalty. But it’s disrespectful. The implication is that your son can’t be trusted to make reasonable decisions about his own life and body without being bribed into them.
“Because what’s now called Class III obesity carries serious health risks, your son has good reason to pursue the effective treatments that have become widely available. You, in turn, have good reason to urge him to do so. And no doubt you already have. I imagine that’s why your husband has concluded that your son won’t do what’s necessary to secure a healthier life without pressure. But not only does your husband’s plan treat your son like a child, it also may not be effective in the long run. After all, once the deed is in his name, your son can simply discontinue the program.“So consider another gift, the kind where the condition is intrinsic to what’s being given: Offer to defray the costs of his treatment. You have the means, and this way you’d be giving him something without saying anything about how much you trust his judgment. He may still decline. If he does, you’ll need to make your peace with the fact that it’s his body and his life.”
Bingo.
Ethics Alarms 
This reminds me of a situation at work, or the old manners rules about not giving unsolicited advice.
We hired a 17-year-old recently. She really likes the movie IT and the clown Pennywise (I don’t know if you’ve seen the movie or the show). In a pretty sharp tone, my boss told her she needed to stop liking that and get a new hobby. My boss hasn’t established much trust with her, and she’s only worked with us a little over a month.
She is now resentful and hasn’t forgotten it. The value of respecting autonomy matters, even if the person is a teenager with a movie taste you don’t personally like. My boss is blaming her for being too sensitive.
As a two track professional in theater and law related services, this has been a theme in my life, not always with a pleasant outcome. More than one boss, client or supervisor told me that my artistic activities occupied too much of my energies and time out of the office, and my response has been always the same: This is none of your business I don’t tell you how much time and passion to devote to your family, your church, your charities, to golf to your social engagements, and won’t. The fact that you read a review in the paper of a show I directed doesn’t give you any right or authority to assume that actvity affects my job here.
Then I sang this:
Ha. That’s a very apt reply!
Please tell me you are joking. You sang that? As your boss, I would not have fired you. Nope. I would, though, direct you to relax in this little room equipped with nice, friendly, cushion-padded walls. At the very minimum, I would expect you sing this:
https://video.search.yahoo.com/search/video?fr=mcafee&p=animals+it%27s+my+life&type=E210US739G0#id=1&vid=c546eaca157bd113c8ae927187ff78f2&action=click
Lesley had to fight for that dark song. The record company was worried that it would ruin her perky reputation. Turned out to be one of her best…
My favorite of her hits. The redeeming rejection of “That’s the Way Boys Are.”