The justification I have seen is it gives an opportunity for some who would never get the recognition without it. Some say without the threads, the only guys who would be recognized are those in their 20s, extremely good-looking, with 8-pack abs, body fat less than 7%, and a minimum of 17" arms.
I can understand it, but the problem is there have been guys who have received the honor for whom I can't see a valid reason. They are friends with one of the few guys who like to start such threads. As a more extreme example, one guy was at least 80 lbs overweight and occasionally rude in the forum threads and from what I could tell, never in any of the fitness related threads. This is a fitness site, remember. I wouldn't condemn the guy, but him being MOTD diminished it for those who receive and deserve it.
The threads are often started by a very small number of guys, who I think are doing it mostly for their own need for visibility or need to show some control. The threads are not campaigns, where honest pro and con discussion ensues. Negative comments would be unfair to the guy who may not have requested the thread in the first place, but it ends up being a cheerleading thread only. Anyone saying anything even questioning the selection is condemned by the forum "police".
I'm wondering if the threads actually motivate voting for another contender.
I've spent too much time on this topic, but maybe a solution would be to allow that both pro and con discussions are ok, so the thread starter gives some thought to that, and also encourage the con messages to not be too severe, to minimize any humiliation to the guy. Not that it could be enforced, I'd like to see limits on the number of such threads any one person starts.