Government doesn't have "rights." Government has "authority." Does the state of California have the authority to ban trans fats from commercial sale? Yes. It almost certainly does. The general area is traditionally one State's have actively regulated. However, if the Federal government decides trans-fats should not be regulated, the Federal will is supreme.
Is California's ban on trans-fats a good idea? From my understanding of the subject the current understanding is that trans fats serve no useful purpose and are a serious long-term health risk. However, that "current understanding" is fairly new, the degree of immediate danger seems low, and the weight of the evidence is not overwhelming. I feel the State acted prematurely and should have waited a few more years.
Personally, I don't use trans-fats in my own cooking. However, we're not above stopping at fast food restaurants now and then or sometimes buying a pack of Little Debbie's "creme" filled oatmeal cookies. Since we are consumers, I'm happy trans fats will be removed from the foods.
Regarding some of the other arguments:
"Labeling" does not provide protection. The foods are still overly harmful and, for the time being, are attractive. In fact, there's a parallel doctrine in civil law called "attractive nuisance," and the owner of the nuisance has the responsibility to render it safe from those who would find it attractive.
Yes, there are other products in the marketplace just as or more dangerous than trans-fats. So? What's your point?
When food isn't regulated, producers put a lot of very bad food in the chain of commerce. That isn't conjecture, it's historical fact. Since Sinclair Lewis wrote "The Jungle," human and corporate natures have not been repealed. Food must not only be regulated, but must be inspected by agencies with enough inspectors to do the job and the desire to enforce the regulations. Again, not a conjecture. Food inspection in the US is at a low point now because of the sentiments of anti-regulation ideologues in government and their industry sponsors. Failures of inspection, failure to identify sources of contamination, and a variety of other scandals are regular "news." Coincidence? Europe functions very well thank you with a high degree of regulation. Large Asian countries without meaningful regulation, not so much.
If you want to eat downers, that's your business. Raise your own cattle, infect them with something horrible, slaughter and eat them yourself. I want government to Keep them out of my market and off my plate. That and the salmonella infected spinach.