Richard Stallman on The great divide between free and open source software:
Without these freedoms, using software presents people with ethical dilemmas. If a neighbour sees you running a program, realises it would be useful and asks for a copy, what do you do? If the program isn’t free, you have to choose between two evils: either be a bad neighbour by not helping, or violate the software licence. The latter is the lesser evil, he argued, because the organisation supplying the software has already done something bad to you by supplying proprietary software, but you would still be going back on your promise. Furthermore, you are spreading more copies of non-free software that will present a similar dilemma to the recipients. The answer, said Stallman, is to only use free software.