I say keep it up. They leave all those mags because they want to get their numbers up, not because they care or anything. Very few people have ever converted from simply reading the mags. Most of them convert because of strong pressure from JW's themselves. I woulnd't worry that your encouraging them to spread the word and gain converts.
Am I only encouraging JWs?
Yeah! Put some kind of warning stickers on those magazines! They are, definitely, dangerous. You could have all kinds of stickers, like: "This cult breaks up families", "High Control Group. You won't have a life after you join.", "They hate everybody", "They don't believe in higher education"....on and on...
Like someone else said, the Witnesses that are bringing the magazines think that they have someone who is interested in reading the magazines, which is why they keep bringing more and more. I guess, either way, you may be saving someone's life.
I threw all away except for a couple and I stuck post cards into those with xjw website info
Why do they put in such old magazines? These were dated 2002.