The point is not that free software programmers specifically refuse to accept wrongly indented code, the point is that they often refuse to accept code based on wholly arbitrary reasons. Arguing that indentation really isn't an arbitrary reason is fighting the hypothetical; replace it in your mind with something that is.

There's also the "we won't accept this bug report unless it fits this list of arbitrary requirements" gambit (if you actually do manage to submit the bug report following all the requirements, it will still get ignored anyway, but doing it this way they can artificially deflate the number of unfixed bugs and blame things on the user for not following the directions)