Better to make sure the company gets it so they have to pay someone to open it.
Do you have a source for this? What do they do with it then?
The only ("only") problem I personally have is that it generates soooo much waste. It is always so frustrating checking the mail, and immediately dropping 10 or so sheets of paper in the trash before I even close the mailbox (the safeway mailer is especially bad at this...)
I once when I lived in a rural area, with a small PO received a despicable scam focusing on elders, containing a return-postage-guaranteed envelope. The postmistress couldn't provide direct instructions, but enough for me to surmise that anything I could actually fit in the envelope would work.
I filled it as full as possible with thin lead sheet (often used for flashing around chimney-roof intersections), a bit of reinforcing clear packing tape around the edges, and a nasty note. When I brought it back for mailing, I got a bit of a smile and assurance that it would go properly.
Satisfying, and if everyone did it...