There is still no proof though that tether really is a scam, but assuming it won't be exposed until there is a run on the bank ie bitfinex.

There is a possibility that it is a scam however they earn more from their legit exchange business in the long run than they ever could with tether so if they are scamming then they aren't being very smart.

For reference they have about $1 billion of daily trading volume and if we assume an average fee on both buy and sell of 0.25% means they gain about $2.5 million a day, or around $900 million a year. A $2-3 billion windfall would certainly be nice for them but they will make that kind of money easily in the next few years anyway.