I am 100% for mandatory posting of calorie information. Here's just a dumb example.
A year or so ago I was in the financial district of San Fran - so I went out to lunch with a client to the local chain restaurant because the lines were long everywhere else.
I avoided everything bad - so I thought - and got the salad with grilled chicken and raw veggies with the dressing on the side. The dressing was listed as a vinagrette.
I ate about 1/2 the dressing and the whole salad. I get back to the office and look up the calorie info online.
I literally would have been better off getting a Whopper at BK. The salad had 2,000+ calories and a shiat-load of saturated fat in the so-called "vinagrette" dressing.
I don't agree with mandatory. How about letting the free market decide. Now that you have had that experience, you won't be eating there any more. As a result of business dropping off, the restaurant will feel compelled to offer their nutrition information for their menu or, they could resist and it would be at their peril when nobody eats there.
All without government involvement.