Gross. I think the theory behind blank slate is to be what the client needs you to be. I don't think it's supposed to be a license to be creepy and weird.

I'm not sure you can blame your ex-T's issues on the blank slate approach. But I do think it's a great idea to explain what didn't work for you in previous therapies so that you can observe how a potential T reacts to your negative experiences. I find it either interesting, entertaining, or both to criticize their unknown colleagues/and or profession. And I've interviewed quite a few, maybe 2 dozen, potential Ts. The ones I have always ended up working with are not those who blindly defend T itself or former T, and not those who act exaggeratedly horrified, but those who calmly and straightforwardly talk to me about how they do things.

Good luck!