It is gross and unhealthy. I did it for years, at first because I didn't recognize the problem -- and also because I had to grow into some security in both my self and the relationship in order to push back. Later, we spent a couple years with me pushing him to change, and him saying that he would ... but then not actually following through.

When I finally completely burned out and threw in the towel and refused to 'mom' anymore -- by this point I had joined a web community of stepmoms without their own children, who suggested this as a useful tactic of last recourse -- my dude actually abdicated his custody rights rather than take on any more work or responsibility. (By this time the older kid was in college, so only the younger was affected.) So kid went to live with her mom full-time.

Not the way I would have played it, but ... (shrugs helplessly) I couldn't force him to be better.