First, I am not a super strong proponent of this. I am kind of ambivalent but like I said, leaning towards being supportive.
You can argue the regular season is devalued but honestly, the teams from 69-128 are all or almost all going to lose immediately, and then you are going to have the same setup you have now. As the tournament expands, the value of the regular season becomes less about making the tournament and more about positioning yourself for success in the tournament (by getting a high seed). I don't think it is a big deal.
The pro here is that I think every time the NCAA has increased the sign of the tournament, it has driven more interest in the sport, more investment and more excitement for those participating or competing to participate.
If we did this, I think it would ensure that all the mid majors who had good seasons would make the tournament. We wouldn't have a Belmont, who went 26-4 and got upset in their tournament championship game, left out. Teams like UB, who made a great run late in the season but ran into a buzzsaw with Ohio in the MAC finals, would still get in.