If by "you don't have to" you mean that Medicare does not mandate it, you are correct. But that's not the point. Medicare so dominates the market and the health care environment that there isn't any practical alternative so, effectively, you "have to." To say "you don't have to" take Medicare B is like saying you don't have to leave your house to get medical care or you don't have to have a government-issued ID. Try living life otherwise..

Which is why, unless you are well up in the one-percenter ranks, you have to have Medicare.