The opportunistic attitude displayed in looking for an excuse to keep items found on the field without making even a modest attempt at locating the original owner reflects a lack of any sense of community with fellow disc golfers.
My wife accidentally dropped her phone on the course last weekend. After nearly 2 hours of searching, we were lucky that one of the many nice groups of players (there were a couple of real jerks too) locate it and return the phone instead of one of the "Score! Found me a Droid, bitches!!!" crowd that appear to be in this thread, elsewhere on this site, and in the game.
If it's obvious that the person who left the item is no longer on the field (i.e. you're the only one on course,) then pick up the litter. If there's a lost and found, put it there. If not and you find it usable, then put it to use.
If there are other people on the course and you can't be bothered to ask around about it or put it in the lost and found, then either leave it where you found it or come to terms with being a thief. If you chose the latter, then you'll also need to accept the fact that you're only going to receive approval on such activity from other thieves. Thankfully, you appear to be in the minority.