If you get lots of important items 6 days a week via first-class mail then I can see you having the perspective of junk mail is actually subsidizing this important service.
However, my guess is that most people don't. This is based on my own lived personal experiences and those of the extended network of people in my social circle. It's not made in a vacuum. Therefore common sense is that we're subsidizing an errand of cleaning trash out of our mailboxes several times a week.
I get that people are sensitive to government services under the current political climate but there is no reason we couldn't cut back service to say 5 days a week instead of 6.
[0]https://stateimpact.npr.org/new-hampshire/2011/09/27/how-jun...