I'd go for a tattoo in a discreet place that could tell me these things, if there were a bit of granularity to it - knowing how stressed you are us useful for learning how to be less stressed, and in general it'd be nice to have some diagnostics about my body easily at hand like that.

As to using them to stop people from doing things... on the one hand I see your point, on the other hand it seems like it'd be a big violation of privacy to require tattoos of that sort, especially if they were in an obvious location.