“Have you committed” is really a misnomer. They closed the mental hospitals a couple of decades ago (right before the number of homeless went through the roof). People aren’t “committed” anymore. Nobody wants to pay for it.
But if you told someone in the medical field that you had specific plans to harm yourself or someone else, then yes, they would have a professional obligation to seek treatment for you. It’s called an “emergency hold”. That’s just the nature of their job, it’s a requirement of being licensed. Kind of like the way childcare workers are obligated to report physical signs of abuse.
Y’know, if someone posted something like that HERE, people would act. We just would, it’s an ethical obligation.
There was a lot in the press about psychiatric treatment recently, because of the shootings at Va Tech. Laws vary by state and situation, but a typical emergency hold is roughly 72 hours. Just long enough for the crisis to pass. Doing more than that, intervening in someone’s life against their will, is very, very difficult.
The only people who “are committed” are people like Andrea Yates, who drowned her children. Convicted criminals are occasionally committed.
To the best of my knowledge, and again IANAD, specific threats of violence against yourself or someone else are the only red flags. Hmmm, or maybe hallucinations? I don’t know, perhaps if a patient is hearing voices and talking back to them, perhaps then a doctor will do something even if the patient doesn’t want to. Probably depends on their insurance 
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OTOH, I don’t think there are any kinds of “abnormal” ideas, or thoughts, that come up in therapy that cause the therapist to act. I think they’ve pretty much heard it all - sex with anyone (or anything), hatred, love, fixations, quirks, phobias, fears.
But I can understand fearing that our intimate thoughts will be rejected or mocked, or land us in trouble. Especially if you’re someone who’s avoiding relationships and trying to fake perfection. I used to feel that way myself.
Typically I wouldn’t bother with bothering you on this, because it’s absolutely your free choice to live an isolated life. I don’t see anything inherently wrong with it.
But you describe a perspective on the world that isn’t entirely accurate – and I wonder if those inaccuracies are guiding your choices. You seem to assume that being in a relationship (whether therapeutic or romantic) means being controlled and learning to hide flaws. That isn’t necessarily true at all, BUT it IS sometimes true of dysfunctional families. It IS sometimes true of abusive parents.
And then, it’s my experience that we DO tend to find what we expect. We tend to interpret our experiences based on our assumptions, so our views are corroborated more often than not. Sometimes we wind up trapped by preconceived notions.
If someone wants to challenge their assumptions, therapy is an opportunity. Posting on a messageboard is another opportunity 
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