It's certainly preferable to not have to double up bedrooms, but we have to remember that our parents did it just fine. I grew up in a family of 6 in a 1600 sq ft house. It worked just fine, but we'd look at that today and consider it unacceptably cramped.
Demand for space per occupant has risen. It doesn't make sense to expect our parents' price tags when we're demanding larger properties.
There's some evidence that kids who share bedrooms have better social skills.
Historically, the concept of separate bedrooms is very, very recent.
The expected size of bedrooms has also risen dramatically in the last few years. Some are even bigger than the living rooms of houses built in the 1970s.
Demand for space per occupant has risen. It doesn't make sense to expect our parents' price tags when we're demanding larger properties.