If he ever finds his business failing, then maybe you could go into partnership with him. You can drive him round and wait for him whilst he takes advantage of people, elderly, families, who have left a window open, and give him the thumbs up as he nicks anything that takes his fancy.
He is committing a crime, and anyone who stands by and says nothing is just as guilty. Because there isn't an individual named in the theft, doesn't make it any less of a crime. If you inform the authorities then no, it would not make any difference to the national economy, but multiply by 1000's what is happening with your BIL up and down the country and you're talking significant amounts.
If you or your family were a victim of crime, if someone burgled your house, or assaulted you and the judge let them walk away scot free because to punish them may disrupt family life, what would you say?
If you saw an old lady mugged, would your attitude be 'I've nothing to gain from reporting it'?
If your DC pinched a computer game from a shop, would you just let lie?
The only person you have to justify your actions to is yourself. Please ask yourself the questions above, and you alone will know what to do.