I think you have to remember that many people parent in a style that is not in the best interest of the child, but in their own best interest; When together, my ex was very disengaged as a parent, and has now taken on the role as peer/buddy; to the extent that he allowed a then 11 yr. old to smoke and provided him with such, because it made the "kid happy" - this is just ONE example of the lack of boundaries. I didn't have the energy to fight with the older child, he went to live with Dad - result, he is almost 17, no job, quite school with a grade 8. Both my sons resent my rules, expectations, boundaries etc. and are very verbally abusive to me - and very disrespectful to most authority. I fought tooth and effing nail for the youngest and continue to do so. He has Conduct disorder so is very oppositional to authority - yep, ME. Dad isn't authority, cuz he doesn't show any. Is it hard, damn right it is ... but I have the responsibility as a parent to do whatever I can that is in the best interests of my child. Sometimes, the best, most logical and rational thing is the most difficult to do. This is just my humble but very battered opinion.
I tried the whole co-parenting thing and would suggest that if you can do this with your ex, do it. I wrote a proposal to his lawyer, leaving no stone unturned, whereby there would be CONSISTENCY AND VERY SIMILAR STRUCTURE AND EXPECTATIONS in both homes. That is what is best for the kids and it significantly shuts the door on the manipulation that they all figure out real quick. My lawyer was very impressed and suggested I market this proposal...my ex? refused, because it didn't meet his needs...and it would require communication between he and I (which now I know would have been real bad).
NO MATTER WHAT, PARENTING IS THE HARDEST JOB IN THE WORLD AND OFTEN THE MOST UNAPPRECIATED!!!