It would restore balance to their decisions. Before Trump the court was basically 4-4-1, now it's 6-3 with Roberts occasionally being a swing vote, but not really.
At this point the 6 that are there see fit to use the Constitution to edge the country closer and closer to a theocracy, and of course that's music to many conservative's ears. Both with that school prayer case going 6-3 and Roe v Wade being overturned. The forced-birth argument is just always going to be a religious one, regardless of how feebly some try to hide it. And it's the same with the rulings regarding same sex marriage and yes, even interracial marriage.
What needs to happen is Biden needs to add 2-3 more Justices... hell, barring political reasons I'd say just add 4. Conservatives will cry about it, but they'll cry about anything. Then when the GOP has power they'll do the same thing and it'll be reciprocal. At some point there will be 50 Justices hearing the cases and it might actually make more sense as far as seeking a consensus on important legal matters go. That and maybe both the Democrats and the Republicans will see how the road they got there was stupid but necessary and pass an Amendment giving Justices a 10 year term limit or something. Judicial Review should not be up to 9 people who aren't capable of being held accountable. Just look at Thomas' conflict of interests over the years, he doesn't give a fuck because he's untouchable.