I had an unstable family and a lot of patchwork in my youth. Won't recommend it. It doesn't have to be negative, but it often comes with compromises. And children aren't stupid, they can leverage the conflict of their parents, but it isn't necessarily for their best in the long run.

I heavily dislike the illusionary idealism from some for something that can be quite a lot of work. The state of marriage is pretty much not relevant though. At least in my opinion.

Yes it happens, but isn't the rule. On average, it's ideal to have two happy, loving parents. But only on average!

Thinking in terms of averages and correlations should not justify absurd oversimplifications.

The average human being has 1.99 eyes.

It seems you might be missing the larger point and getting hung up in pedantry. Try taking a deep breath and a step back to consider the bigger picture.