1) if you intend to play self found anyway then this doesn't apply to you. If drops are balanced around you being self found then flippers mean nothing as you have an option to not deal with it. Also, flippers were not the majority of traders. They are getting brought up entirely way too much.
2) they can do this anyway. They can balance the game around you not trading and leave trading in. Keep in mind also the AH is gone.
3) they can do this anyway.
1) But if they balance around self found with an AH in existence, then anyone who uses the AH is going to be geared to the gills in a few weeks. And then in teamgames and the like, this becomes the expectation.
Power in D3 is always relative and part of the fun is building a powerful character in relation to others. Playing 'optimally' is always going to be a big part of the experience. And if you have free trade, then free trade becomes optimal - especially since we will be getting PvP at some point.
2) Trading is a problem in itself. It does *ugly* things to a community. Remember how predatory the D2 trading community was regarding scamming and doing everything possible to get the advantage of someone?
On the other hand, if they implement a trading lobby...you've really just gone back to an AH with more logistical overhead.
3) If they do this, then anyone who trades/AHs is going to be able to pulverize the game far too easily.
Finally, one thing to keep in mind is that rares are still going to be potentially awesome. Some of the datamined affixes are just off the hook. As things stand, you can still trade and potentially trade amazing gear. The very best or customized pieces will be BoA. This seems like a very fair tradeoff.