I have five young kids. There's no way to survive this as a parent if you don't let your kids cry themselves to sleep at times. There simply aren't enough parents and time to go around otherwise. Every child is different, but my five only cried for a long period for about 2 weeks or less. Then it generally reduced to about 30-90 seconds. Over the course of their first year of life, they learn to sleep, in stages. There are regressions associated with certain development stages, but so be it. My family size was average until the last 2-3 generations. Is is abundantly apparent that the reduction in family size provides the luxury of a lot more choices in parenting. That's a positive thing. But because there is so much variety to the human condition, it is illogical to suggest that 'crying it out' is new or terribly sub-optimal.
I have seven children. We almost never had to let a child cry themselves to sleep, but I do suspect that may have to do with our kids' individual wiring and that crying to sleep might be the best solution in other situations. Most of our infant sleep problems were resolved when we realized our kids were much hungrier than experts predicted and started feeding them a lot more! Giving the baby another bottle turned out to be the number one way to get our babies to fall asleep with less fuss. When they get a little older (around 3-4 years) there are occasional times when a temper tantrum goes right into sleep.