The reason I'm personally wary (and many others in the cryptocurrency/ethereum community) is that they decided to add Ethereum Classic trades one night, in the middle of the night when everyone was asleep, They did this without any prior announcement, and no one had any chance to prepare for it, so Ethereum holders suddenly lost a bunch of money in a price drop. It was a sudden and selfish move that might have involved some insider trading to make them come out ahead.
They basically did some shady shizz.
Thanks. Can't be too careful these days.