I remember when I first started betting offshore in 1990 with Bowmans when they were still booking out of Manchester, UK. British law required a 10% WINNERS TAX be taken out of any winning wager. Thus, you were paying DOUBLE VIG on any winning wager. Talk about an impossible beat...I think it was Scotty Bowman himself that got legislation passed a few years later that waived the "winners tax" on foreigners, and Bowmans really took off after that.
I believe British citizens still pay a "winners tax" on any winning wager, just a like a sin tax on cigs, gas, booze, etc. in the US. That example is one compelling argument AGAINST regulating sportsbetting as I am sure the feds will add on all sorts of taxes against our "winning" wagers should sportsbetting ever be legalized and regulated.