Why would you assume that people who don't have full time work sit around and do nothing?
I'm the breadwinner for someone who stays at home and she's immensely valuable. A fact I'm quite aware of as she just left for a few weeks on a trip and now I'm working and doing what she does. She does all the house chores, picks up medications/runs errands, is trying to get a business of her own off the ground (is making ~500/mo with potential to scale if she's allowed time to actually do it), etc. She also contributes a lot to making sure our household is embedded in our community, which in turn enables us to both more efficiently help others (when we can) and to receive help when we need it without relying more on the government/taxpayers. She does the work required to do things like help our parents when needed (we're siblings), which would otherwise be paid caregiving paid by, you guessed it, the taxpayers! She also makes me a way better worker because I'm the one person on my team who actually can focus on work all day and doesn't have to frequently step out for life things.
And this is without children in the home.
Not to mention students, people with disabilities (some of whom may end up being a greater boon to society if they're allowed to reskill or be pickier about jobs rather than being forced to work themselves to the bone until they can contribute nothing + their medical needs end up being worse than they would have been if they were accommodated in the beginning), etc.
The idea that the only way people can contribute to society is via paid employment is a sign of a lack of creativity.