What a political and racist comment you are quoting. Maybe you found it in a newspaper.
To 'act upon' is to behave, to act from the basis of something. So if you tell someone something derogatory (bad) about them, e.g. a parent or a boss saying bad things about the child/worker, then do not be surprised that the child/worker will behave like that, (that they are a naughty child/ a lazy worker). If you tell someone what (you think) they are, they will 'act upon' that basis; they will incorporate that information and behave as though it were true.