step parents don't get to choose how the children are raised which can cause no end of issues and frustration
You think a step parent should have a say in how someone else's children are raised? (And I speak there where both parents are alive and involved, not where there has been a death or some kind of court action that has effectively removed one parent).
is whether or not you had choice in the matter the driving factor in whether you should be allowed to harbour private, negative feelings involving kids, or is it the imperative need to rise above and protect them from that, which is so often applied to step parents?
Your expectation seems to be that not only you get a say in how some else's children are raised but that also the other parent (who has no choice or say in who is in their children's lives) should just shut up and put up? I mean, I do broadly agree that rising above negativity is an important factor in all dealings post separation and divorce but again, you are suggesting that an ex partner should somehow be responsible for caring for people and children that in very real terms are nothing to do with them. I wouldn't, in very general terms, go out of my way to cause upset to my ex's partner and her children, but I would do whatever I considered necessary to secure the health and well-being of my children which may, or may not, impact the new partner and children.
You are ignoring the very important bottom line which is as a step parent, you are making a choice to be in a child's life and an ex partner has no say in that. It is not the same situation to be an ex partner and to want what is best for your children and to want to fight for that (although in my experience, the path of least resistance and not fighting for something you have no real control over is pretty much the easiest way to do these things, I don't blame some people, in some situations, for pushing for what they consider to be fair and just. For example, I will continue to push for child maintenance even though the ex hasn't paid in 14 years because that is what is right for my children.
I don't really care that my doing that makes the new partner uncomfortable or that if he were to pay, it may impact her and her children's life with my ex).
You seem to be suggesting that I should really have learnt my lesson after 14 years and stop fighting for child maintenance and allow my ex to live his life as he sees fit because my keeping on about it is upsetting to his ex partner and her child. You are asking me to forgo my peace of mind and my children's financial security so that the ex and his new partner don't have to keep on worrying about that bigger picture because the hassle and upset it causes is too much for them.