There is no reason to mix coins other than to hide your transactions. I'm not passing judgement. Who wants to pay taxes or be busted buying drugs? That doesn't sound like fun to me.
Seriously?
You wouldn't mind people knowing your salary?
You would be ok with your bitcoin company's profits being calculable from your payments to suppliers, customer receipts, etc?
Why not, everyone that wants the info on my salary can get it now anyway. In fact, if they can get my SSN they can get my tax records too.
I'm fine with business transparency. One of the problems we have with modern business is the lack of transparency. That's also one of the biggest problems with government.