I don't think these acts are inherently wrong. However, there have been (and continue to be) a number of people and other organizations that use "random acts of kindness" as a means of manipulation (telemarketers, ad agencies, Hari-Krishna's, etc.), and so our culture as a whole has become suspicious of such acts. I have a book, "Persuasion" by Cialdini, that you are welcome to borrow that talks about influence technologies, what they are, how they're used, why the triggers are there in the first place, and how to cope with it. Acts of kindness generally help set up a culture of cooperation and reciprocation. This may also be making you feel uneasy, as there is no obvious way to reciprocate, and thus you may feel obligated to them in some way that they may call upon later. This is further complicated by our increasingly heterogeneous society with divergent customs and expectations.

Anyway, that is my 2 cents. :)