It has definitely been *correlated* (causation AFAIK has not been found).
The link isn't certain; dieting alone is connected to obesity via several connections (including psychological and physiological, especially hormonal). There is, at the most basic of levels, the fact that a person who is dieting is likely to already be struggling with either a weight issue (ergo is more likely to gain weight than maintain it) or an emotional/mental health issue (can go either way, anorexia or binge/purge, binge alone, etc.). Dieting is restriction; the natural reaction is to binge after a period of dieting, which can be as short as a day.
Lather, rinse, repeat.
I have read the reasoning that the body "doesn't know what to do with" an artificially-created agent. That that agent would somehow be converted to fat hasn't been proven. Actually, the body's most typical reaction to what it perceives as a foreign agent is either to attempt to expel it or to put a lot of fluid around it so that it can't harm the rest of the body. So fluid, yes, potentially; fat, I'm not seeing the scientific support.
Is it good for you? No. That's why it comes with a label specifically stating that. And people make that choice.
Would I personally prefer natural alternatives...yes, and I choose them. Note that I said *choose*.