What kind of shelling point would you propose to decide when people should have to add a label?

When a new food hasn't passed safety demonstrations comparing it to old varieties. Either by demonstrating that it's chemically the same (i.e. I don't care if it had an extra gene causing it to grow quicker); or by studies in people, just like for new medicines (the kind of studies that have to prove safety, not to prove efficacy).

Of course, lots of foods introduced throughout history and which keep being introduced today aren't up to these standards; they just don't happen to be genetically modified using modern technology, so no-one asks them to demonstrate their safety. I think the difference between what's required of old and new tech should be smaller.

I think that transparancy and free flow of information is vital to dealing with risks arising from new technology. I don't want government burocrats who think it's best to keep new technology that has an effect on people secret because the people might not like it.

I shouldn't have used the word "secret"; I don't want things to be classified or lied about; I just wish, counterfactually, that such subjects wouldn't gain widespread public interest. I don't trust mass public opinion and lobbying over government bureaucrat decision making in technical matters and I'd like to have some combination of transparency with rational decision making.

For almost every product sold, food or otherwise, it's probably possible to come up with a factually truthful label that would scare away customers. But even socially powerful causes, like that against cruelty to animals, rarely get what they dislike labelled ("this product made with factory farmed chicken"). Shoes aren't labelled "made in child sweatshops". Software isn't labelled "written on the Shabbath".

I'd like to keep it that way. The political-social game of putting shaming labels on things based on lobbying success can do a lot of harm to everyone if it goes far enough. Labeling requirements should be restricted to a very small set of very clear rules, e.g. those about potentially causing physical harm.