But that's why a like button would be helpful. It's common courtesy to thank someone for help and a like button would at least curb people just littering threads with pleasantries.
It is an option, but I haven't reservations about it.
What real purpose would a 'like feature' serve, to show how many people appreciated your contribution who may not have any smerits to give at the time?
If there's no means to earn the likes would it not turn out to be an unnecessary metric that would be giving at the slightest whim without careful consideration? Users earn merits and by extension smerits, so they would try to be very careful in giving the out, likes on the other hand would be easily overused.