I don't know many young people that agree with that. Families, sure, east and north side is better for schools and such, since it is basically suburbia.
I have a family and live in the east side :-) I've seen it a million times, people move to seattle, get an apartment, then couple up and buy a smaller condo, have kids, need space, move to the evil eastside.
Well, who knows what it will be like in the future. Seattle isn’t losing population, some more suburban part of Seattle (e.g. West Seattle) are booming also. It is possible that millenials will stay put and not migrate to the east side.