People should have a right to know what is in the food they're purchasing, regardless of whether I think they're being paranoid or not.
The "if consumers see the GMO label, they might think its bad for them" argument is a f**king joke that libertarians would make. GMOs are (pretty much) safe as far as we know, but the argument against allowing that to be on food labels is to basically say the stability of the holy free market is of higher consequence than a basic consumer right.
Nobody's said anything about "allowing that to be on food labels". People can put whatever they want on their food labels as long as it's not false. Do you not see the difference between "allowing" and "mandating"?