I hear people say that fairly often. Usually it's said either when somebody is doing something difficult or dangerous to him/herself, or when somebody commits some atrocity on somebody else. Like, for example, tries to swim from Africa to Spain. Or blows himself up in a crowded cafe. Or cuts off her husband's dick.
Because people are always so rational. Like, for example, one acquaintance of mine who went and got himself circumcised as an adult. No, there was no medical reason. Or religious, for that matter. He just noticed that some organization was doing circumcisions for free, and figured: why not, what the heck, maybe it's fun? (In case you are wondering, it wasn't.)
Or, for example, some old classmates of mine who used to beat one girl up every day, just for the hell of it and just because they could. Once I stood up for her, also just for the hell of it. The people who were beating her up did not want to fight with me, so they said "sure thing, no problem, we'll find somebody else to beat up". Probably they had a very good reason, it just wasn't very personal.
But - irrationality aside - what really amazes me is that leap from the doer's good reason to the speaker's good reason. I am sure a lot of people do a lot of things for reasons they consider perfectly good. Pol Pot had what he considered a good reason to kill 20-25% of his citizens, Microsoft had what it considered a good reason to slow down Vista network performance during audio playback, my downstairs neighbors had what they considered a good reason to play music at a rock concert volume. The question is: why should anyone else consider those reasons good - whatever they are?
And the reason this bothers me so much is obvious: if doing exceptionally vicious, dangerous or masochistic things earns people understanding in and of itself (because nobody would do that without a very good reason), it will encourage people to do vicious, dangerous and masochistic things. For a very good reason.