But when the endstate is "becoming a better person" (which IMO is both undefinable and a copout for lacking martial skill), how one measure that?
I think this is a big part of the issue. It is mostly subjective. Maybe it would be possible to take a population and measure that some how they were less likely to fight, they were arrested less often, and were charged with spouse abuse less often. I think though that you cannot draw that correlation or inference as you could also argue that the individuals self selected themselves out of the pool and would have reached that anyway.
Maybe some of our psychologist friends can shed some light that it can help alleviate stress, I think we've determined that exercise is good for you in general...but that too, doesn't uniquely ID that martial practices are special in this way.
So, i suppose you'd have to do a completely subjective survey of practitioners and ask them if they thought their training made the a better person. Again, though does this really count?
I personally don't care. to eaches own. If they like what they are doing then let them do it!
If you don't like what they are doing, then don't do it. I think it is as simple as that.