You don't want to take away his pass catching skills or opportunities.  You do want him to be an effective blocker so that when you aren't running a pass play he's more than just a decoy, but someone they need to account for as a blocker.  Then when you do send him out on a pass play, he's more effective because they had to account for him as a blocker, so they couldn't just try and play a physical safety on him.  You want the other team to have to make a bad choice and if he's an above average blocker, there is no good choice for them.