You should be able to make a friendly competitive bet with your mates or coworkers or even strangers without getting in trouble. I am even fine with businesses facilitating this with apps or whatever. But I don't think anyone should be able to bet so much that it could make it hard for their social financial obligations to be met (taxes, rent/mortgage, utility bills, child support, etc). Otherwise society ends up having to help feed, house, clothe, rehab these people. You are giving people the choice to substantially wealth and at worst be saved by the social safety net, many people would take that bet.