I guess I thought more about the fame/glory you'd get than love of any particular sport.
Also you could dedicate your life to a sport but still never become a world champion or even make a living doing said sport if you lack natural talent. In the hypothetical it was guaranteed, at least how I read it.
100M dash or UFC champion would be pretty bad ass. Could you imagine knocking all these 20 year olds out when you're 85 years old? They'd be like "WTF?!? Homeboy is old as balls, uses a walker to get to the ring but is one punch KO'ing me! WTF?!?"
I think a willingness to trade your life to be a world champion in any sport is pretty sad, and vacant. No reasonable person would answer yes. And most that did answer yes would be begging for their life back when the "check" came due.
This reminds of something I heard a billion years ago when I was getting certified as a trainer. The instructor mentioned a survey of a bunch of Olympic hopefuls who were asked if they'd want a guaranteed Olympic gold medal, but in exchange, they'd drop dead 20 years later. I think something like 30 or 40% said they'd take that deal.
I guess there's a bit of a difference, a pro or already-top level athlete being offered something like that, compared to recreational athletes and average Joes. Priorities and all that.
It has nothing to do with top athletes v. average joes and everything to do with human psychology and underestimating the "cost" of something so far in the future. This economic error is repeated in other behaviors as well, most relevant to this site - lifestyle habits affecting health. Many people eat the shit they do not b/c they are ignorant of the effects, but b/c those effects are usually far off in the future so they are "undervalued".