People make whatever choices they make based on their own situations but looking "big picture" at the results it's hard to disagree with the statements above. I suppose perspective matters too; I recently participated in a thread by an OP who's DH had been contacted by a 1/2 sib that had been abandoned by their "common" father...OP talked about how THANKFUL they were that the sp**m donor had dumped his first family for her DH's mother, produced him and provided for the "warm and wonderful" life they all had now...I was appalled, but I digress...
There's lots of versions of the "step" story - ours started with DH and his first wife divorcing when their children were tiny. I'm realistic enough to know I don't have both sides, but the fact that their mother re-married 5 weeks after the decree was final must be indiciative of something. This was 28 years ago; before custody and support arrangements were what they are today. Basically mothers controlled kids (especially little ones). Their mother proceeded to build a life with her new DH as if he was their father and simply isolated them from DH and his side of the family like they never happened.
Fast-forward 12 years to the point where DD's were able to request contact on their own (which their mother deeply resented but couldn't really prevent); this is where I came onto the scene. DH had been basically single all that time and was just re-establishing his relationship with them as we courted and married. They were adolescent girls then and it was difficult on every level. Gut honest? They were never MY/OUR children nor could our relationship ever be like that. They also "couldn't put the horse back in the barn" and reclaim all the lost opportunities of the "little kid" years with Daddy, and their pain in this became apparent as the DS we had together went through each of those stages. Were they resentful? Most definitely, but we all did the best we could at each moment to develop the most loving relationships possible between all of us in the context.
We are well on the other side of this now as both of DH's girls are in their 30's with families if their own (6 grand kids altogether) and DS will be 17 soon. We are all "family"

but a far different one than they would have had if their parents had not broken up. They have emotional scars no child should ever have to carry, and no more so than my DH after having been deprived of his children. If he had it to do over, knowing what he knows now, he would have fought TOOTH and NAIL to keep that marriage together and he and I have always agreed that H**L will freeze over before we'd ever put DS through anything similar.
Divorce is not good for children.