I once had a minister caution me about taking things out of dumpsters- he was concerned that I could get into trouble. The funny thing was that he was there dumping stuff himself and the dumpster didn't belong to his church. My experience is people get more angry when you are filling up their dumpsters than when you are emptying them out.

Many people are also happy to see that an item will get another use. Often, it's not people you would even expect to be recyclers - just people who hate waste as much as many of us do.