So according to you: they should give up their paid seat so that you don't have to pay for assigned seats, even when you know way in advance that you are traveling with a 3 yr old?

Let's ignore special cases where you didn't have a chance to buy assigned seats, and focus on the vastly more common scenario where parents can easily pay to ensure seats of their choice.

Yes, it's nickel and diming by the airlines to make all seat assignments paid. And hating airlines is completely justified.

But I find the entitlement of parents, that other passengers should accommodate their parsimonious preferences, just amazing.