If I go to a restaurant, where there's an a la carte menu, and I pay for each item I choose from the menu - starter, main course, side dishes, dessert, coffee, and the person at the next table decides to just order the main course for themself and their child, no side dishes, starter etc, do they have the 'right' to demand that I share my starter, sides, dessert etc with them, because their child doesn't have any of the add-ons? And would others think I was 'disgusting' for saying no?
Basically, airline travel used to work on a set menu basis - you paid the price, and it included all the extras - but it cost more than the basic cost of a no-frills flight now. And now we have an a la carte menu - but everyone knows that that's how it works - and they can choose to go for the cheapest option, or they can choose the add-ons that they need. But if I choose to pay to put a bag in the hold, you can't demand I give you my hold baggage allowance because you haven't paid for one, but want to take more luggage.
Cheap flights are great - last year I flew from Glasgow to London and back, as a day trip, to meet up with MN knitters and crocheters at the V&A - there's no way I could have afforded to do that under the old system, but because I could fly with just hand baggage, and was flying solo, I could pay the bare minimum and have a great day out. But, as I paid much less than I would have paid under the old, set menu pricing system - did I scam the airline? No, of course not - and the airlines are not scamming people when they offer a menu of extras you can choose to pay for. They are giving you choice - it is up to you, grown, intelligent adults, to decide what choices to make. Just don't expect others to bail you out if you make the wrong choice.
As a previous poster says - if a parent chooses to play russian roulette with seating allocations and the needs of their small children, and loses - that is their fault.
And I notice no-one has answered the question from a previous poster - if you do decide not to pay for allocated seating, would you offer to reimburse the person who has, who agrees to move so you can sit with your child - or would you expect them to be out of pocket because of your poor decision?