Board Thread:General Discussion/@comment-99.245.49.23-20141231055157/@comment-25102474-20150111161013

Even if you limit the trading to same rarity levels, it can still be abused in that events where URs are offered for "free" are farmed for the purpose of exchanging for unobtainable UR cards. Judging by how many people seem to have defense teams full of HUR Kiyohime, there are plenty of people out there who are determined enough to farm free URs. It will also trigger more cases of accounts being "hacked" to facilitate further trading.

It would be nice to have the ability to trade, but negative consequences should not be taken lightly, solutions to combat exploits are needed before implementing new features.