Whether we like it or not, paying for seat assignments is now a thing. If you want one, you pay. If you don't want one, don't pay. Whatever. It's fine with me. But, to insist that you get to go on a plane and insist that you get seats with your family together without paying is absurd.
I truly do not understand the mentality of wanting something for nothing.
Your purchase of a fare on a plane only gives you A seat on the plane...not a particular seat. They do sell those, however. So, buy it. There IS a choice. You don't want to pay, which the cheap side of me understands. But, don't say you don't have a "choice." Don't pay, however, and you take your chances. You have to decide whether taking that chance is "worth it." I always pay, and it's not because I want to sit next to my family (we are all adults and near adults and are perfectly capable of taking care of ourselves), but because I prefer a certain type of seat in a certain part of the plane. I consider it part of the "price of flying" to get that seat. So, I pay.