Yeah, the weight is a wash, which is a big negative for tubeless in my opinion. Also, the maintenance is also one thing I am thinking might be bad. Allison runs tubeless on her Superfly and she has to pump them up before every ride. I almost never had to with the tubes. that really bugs me.
As far as hanging out the goo, that's not a big deal.. it seems like I am changing tires a few times a season anyways. I don't mind redoing the goo then since i'll have to anyways.
I was riding Allison's bike on a wicked fast downhill section this year and while turning braking/ landing I also burped the front tire. it scared me kinda. I thought I lost a bead for a second. felt really weird. That's also a negative for me.