I put mine in a empty container marked "used" and use those blades to cut paper until they don't even cut that anymore. At that point, I put them in my Sharps container. It hasn't gotten anywhere close to full yet (with combo of medical needles, sewing needles & rotary blades), but when it is, I can ship it to a special company that will safely dispose of them. I'm not super worried about rotary blades going into the landfill; my main concern is the safety of the trash collectors (I think they're called something like environmental services workers these days) who have been known to be injured by needles or blades because they snap in half during the compactor process & can go flying out and into the workers, causing serious injury and high risk of infection. I guess we all have our different causes.
The cost of the trade-in program is the same as buying brand new packaged Olfa blades from Wal-Mart. If the blades in the linked program are actually new, as in "just off the floor of the manufacturing plant", I'd be willing to switch to them & pay the small premium to be environmentally-friendly. If, on the other hand, they are new, as in "new to you", I'd prefer to keep buying blades that are actually new as they tend to be safer to use.