My impression is that there's a halakha that, if you give food to a Jewish person, you must make him or her make a blessing on the food. If you know that the person will refuse to do so, you may not give the food to begin with. Does the same apply to the bracha acharon or are we free to let people make or not make such a blessing?
Tosfot – Brachot 35a, s.v Tinach l’acharov says that the bracha acharona is considered even more important than the bracha rishona .
Therefore anything that applies to the bracha rishona should also apply to the bracha acharona.
The Poskim discuss whether there would be a prohibition of Lifnei Iver by feeding someone who will not make the appropriate blessings (before or after), or will eat in situations that are forbidden (for example, without washing his hands as prescribed by Halacha).
Upon first glance, one could consider this 'one-side-of-a-river' (a registered limitation to the prohibition of Lifnei Iver, which dictates that the prohibition is only to facilitate (enable) a transgression, not to merely assist in something the sinner could have performed anyway [with the example of giving wine to a Nazir who is on the other side of the river and unable to reach the wine on his own, as opposed to being on the same side and therefore able to access it without your help]), as eating is something that people have the ability to do without you; as long as they would be able to source food of their own, this prohibition does not apply.
However, it seems that this limitation does not apply when creating a situation which creates the desire. For example, a father may not hit his older son, because he is creating a scenario in which the son may hit his father back. In this case, the father is not enabling the hitting, but creating a motivation.
Accordingly, it would only be permitted if the person receiving the food would have eaten anyway. If he is only eating (or eating more) because you are giving him, then you may transgress Lifnei Iver.