How? How does allowing to go into the red cause people to buy more Tokens? Most Managers avoid going into the red, as it does put your highest value player(s) as collateral, so it is a huge risk to take.
I would say that most who do this either already have a lot of Tokens, and know they can buy more $$, or like taking risks and figure the income from Competitions and sale of other players will get them back in black.