There are a lot of companies marketing the ability to do this right now. The science is not there to support it.
Currently, all the experts say that there is not a reliable link between our physical or biological manifestations and those mental states or propensities, but I think the real fear, of course, is that society will come to accept these links, that we'll go back to an age where we thought physiognomy or physical characteristics revealed character and that this new technology will be seen as providing new and objective truth.
I'm not sure that the fear is that it will in fact reveal mental states, but the concern is that it is being marketed as such.