Completely off-topic to the original discussion, but assuming that you intended to imply the quantifier that I think you implicitly intended to imply - i.e., "all people", or even "most people" - you must be living in a completely different world and/or a very cushy bubble. [1]

I expect many people on this site are lucky enough that they can work on whatever they want - either because their interests happen to align with what's currently in demand by the market (as in my case) or because they were lucky enough to be born to rich parents or win the startup lottery.

But take a step back and look outside of that world. Consider, for example, the many people working as cashiers or cleaners. Do you really think that all or even most of them work those jobs because that's what they genuinely want to do, given a choice? It seems much more likely that the main reason why most of them work in those jobs is that they have to make ends meet somehow, and those are the kinds of jobs available to them.

As for the more on-topic part...

Why do you assume that those intelligent people would not engage in some other little value add activity that can make them a lot of money.

I don't. There may be other talent-wasting sectors in the economy (and I guess you always get some geniuses spending their time on whatever the equivalent of card counting of the day is). I have simply pointed out that HFT is one of them (and I do believe that finance in general is the worst offender at this time).

[1] If you intended to imply the quantifier "some people", I apologize for my misinterpretation - though in that case, I would wonder what the point of the statement was. Certainly it doesn't help paint capitalism in a positive light, because every economic system allows some people to work on whatever they want, while the rest tend to have the same superficial choice of job that they do in capitalism. (E.g., you were not simply assigned a job in communism either.)