That is a very bold position to take. given a number of factors, including the baby boomers general under saving for retirement, one would expect multi generational housing to increase in the next 10 to 20 years. This type of attitude will be interesting to see played out as many boomers in their 80s find themselves without sufficient funds to maintain their lifestyle and without family willing to take them in.
There are many MORE and BIGGER issues than just a mooching 20-25yo in their house. It ALWAYS involves a big thieving drug issue, threats and raging fits & hitting, no sleeping at night, cars being taken (mom said I could borrow the car; dad not home -- his word against mom's word), legal address, tenants do NOT have to pay rent to get occupancy rights (squatters rights), etc.
You can NOT JUST change the locks after throwing their stuff in trash bags in the front yard ... you have to legally evict them.
And by the time the boomer parents are 80, those kids mostly will either be in prison or dead from overdoses, car crashes or murdered.
And as for Baby Boomers not having funds for retirement .... those families' savings get drained by their thieving kids, legal fees, therapy sessions, lost jobs (who want an employee with an out of control stalker calling and showing up in office OR no sleep) and multiple moves in RUNNING from their kid.
I have experience with a stalking ex-bf .... think 5 active years and 25+ years of flashbacks incidents .... I think my record was 4 household moves in one year. He and his family thought I should take care of him; my ex-neighbors & ex-friends just thought he was sincere in his love; the state troopers thought he was calm and rational (until he had his hands around my neck). So they trailed him out of town; at least 3 sets of cops told me to MOVE as they were tired of all this crap at MY house (I got gold plated service for a month to get the HELL out of the one town), got no service from the courts as they consider it a domestic matter (I was still alive). And yes, I lost a great job due to his visits, hundreds of phone calls, and my lack of sleep & concentration besides his standing on the sidewalk asking everyone if I was still in the office while begging for change.
"BOLD POSITION" .... experienced position in reality.
Expect MORE rent assisted complexes with senior age restrictions, strong rule enforcement and security guards.
Multigenerational housing --- you ever lived with your IN-LAWs or even your parents for more than 2 weeks? Sounds good on paper; maybe workable until dementia develops or cancer or someone dies or a nursing home wants to see whose funds brought the house or someone gets a divorce & wants their share.