It doesn't mean that discussing it must result in a cancellation of a person though.
Without knowing more context, I interpret the quote to mean that 14-year-olds should be open to having sex with their peers (other 14-year-olds, possibly 13 or 15). Which seems like a position that is not bad enough to punish. It's a very weird thing for him to say, given that everyone knows him for being the president of the Free Software Foundation and not the Sexual Openness Foundation. He should stop commenting on this topic and focus on Free Software instead.
There are more charitable interpretations, but "Stallman wants to sleep with your teenage daughter" is the less-charitable one that political opponents can continue to levy against the entire movement because the FSF won't let him go.