As the child of a crappy father, can I interject something here?
My mother did the same thing. She never bad-mouthed my father. She never turned him down when he wanted to see us - even when he wanted to take me (age 9) and my brother (age 5) to Germany for a summer and she was terrified he may just decide not to bring us back...(this was in the 70s).
And I don't think she did me any favours in letting me figure out for myself what a jerk he is. Really. Even if she had laid it all out for me and I hadn't believed her and run to "his side," (her biggest fear, I know now) it wouldn't have taken long for his true colours to come through and I would have been able to learn my lesson and go back to the parent who REALLY cared about me and get on with my life.
Instead, I'm an almost-40-year-old woman who can't truly reconcile the fact that my father will NEVER be the father I want and need him to be - the illusion of a father my mother tried so hard to keep alive for me.
My father:
Upon hearing I was getting married, he asked me who was walking me down the aisle because "I certainly am not" - even though he was invited and was actually coming to the wedding! I had my oldest son walk me.
When scheduling a 10-day trip to the UK to "include" attending my wedding, he scheduled it so that my wedding was on his LAST day in the country. He also brought my brother and sister-in-law over - they spent the first 9 days sightseeing as far as Bath and such, coming to my wedding the day before they had to leave on a plane early the next morning. Even though my brother and sister-in-law stayed for the meal, my father left almost immediately after the ceremony. Didn't say goodbye. Is not in any of my professional wedding family photos.
When the bombs went off in London, my husband waited 2 days before he finally sent off an e-mail telling my father not to worry, because we were okay - nevermind that he hadn't asked...
These are just the recent things that STILL get to me even at my age and with our history (such as his putting in writing that I was a "slut" when he found out I was pregnant with my first child).
I can't help but think that kids need truth and honesty in their lives more than an illusion of love. Truth hurts - but it's the only thing you can build on.

Just my perspective from my own experience.