There's a long post over at The Sand Trap now - Putting with the Flagstick In - that lays out the case pretty convincingly this proposed rule will provide an advantage to players. Not only that, but the proposed rule will benefit better players, or better putters, much more so than it will benefit poor putters.
If this rule passes and is instituted, people would still benefit even if they didn't change how they putt: the occasional putt that they "goose" a little will hit the flagstick and drop if it's near the center ~1.8" of the hole, when normally it would lip out. Every other putt they would have made… they will still make.
If players adjust slightly to take advantage of the rule, they can make many more putts, due to the advantages inherent in leaving the flagstick in and putting the ball a bit more firmly.
There are a few thousand words over there on that page, so I don't want to belabor the point here: go to Putting with the Flagstick In and read the post there.