I don't think there is anything wrong with playing computers in the abstract sense. A 6k computer makes bad moves and a 6k human opponent makes bad moves and if you never study your play it won't matter whether you are playing GNU Go or not. There are few bad habits you would acquire from a computer that you wouldn't also acquire from a human, if you played both the same.
The problem is that some of the faster bots like Aya or GNU Go can turn a game with no time settings into blitz, whereas a human is likely to take his or her time at certain key points to try to read, if that time is available. You can try taking your hand off the mouse after every turn but it's still difficult psychologically to spend time when your opponent isn't. So bots can encourage unthinking play.
I don't think even weird center-oriented bots like pachi or mogo are bad. If the bot makes bad moves, prove they are bad through play and you will learn something; if you could not prove it, maybe it wasn't bad at all and you also learned something.
Krama wrote:I think humans will be able to learn from go programs even more than chess player learn from chess engines.
Well I can't speak about Alphago vaporware but crazystone has a similar vibe to it. It's analysis is very interesting and I love looking at my own games with it, but you have to be able to pull a Jerry from chessnetwork and say, "That's computer go, I wouldn't play this way." On the other hand, you have to be strong enough to make that judgment in the first place, so there's some bootstrapping problem here (Dunning-Kruger).