I understand sticking with a talented young QB or OT, etc. Those are positions with a learning curve. Players get better. But not Punter. It's not like you have to learn a scheme or new technique. I'm sure there are some coaching tips that can help, but for the most part, you can Punt or you can't. I don't understand sticking with him so long waiting for him to improve.
There's no harm bringing him back to compete in camp but you better have a real competition for the job. There better be real competition too. Sign a real punter who has actually done it in the NFL or even the UFL spring league, not just some undrafted guy from Slippery Rock.
They should tell Harvin that he's on his last chance. He does have a booming leg. He should seek out a punting coach. I'm sure they exist. Get some focused coaching and maybe he can add consistency to his punts.
If Harvin can clearly win the job in camp without the shanks then fine. No more keeping him because of upside and hoping he figures it out in the regular season.