Only 10% of the variance?

Doesn't that make it a single gene with a rather large effect?

" black-balling individuals with the short variants of 5-HTTLPR from becoming traders!" ?

Fewer would oppose it of you had framed it something like: " . . using genetic screening techniques to assure that the professional securities trading pool has access to the most objective and analytical minds."

But aside from that, aren't those people already hired, promoted or fired based on their past performance. And don't those who hire and fire them suffer financially for making bad choices?

In any field where a lot of money changes hands there will be a few who learn to control the cash flow and divert it to their own pockets - and then there will be many millions of others who will eagerly supply them the necessary cash because they believe they will get rich. No matter what you do and what safeguards you put in place the system will always evolve to that state. The large amount of money, our economic freedom and human nature assures that outcome

Human nature operates by resolving subconscious emotional signals to produce behavior. Better "thinking" will never overcome that.