It's an obvious oversimplification, but it be useful to think of measuring the good you do in the world in terms of game points.
Basically, if you're benefiting unfairly from a system since birth, you've started off with negative points. You owe the world something to balance off what you've gotten "for free" (really, at others' cost).
If you hate the system, you recognize the unfairness, and you actively fight against it, you can certainly move into positive points, but you're not starting off the same as people who grew up with the short end of the stick.
So when (for example) the vast majority of the white Australians at the time seemed perfectly happy with the awful system in place, and Peter Norman wasn't, and actually made this statement in a very public way, that was 10 minutes of serious bravery (and then many years of paying for it, afterwards -- which he surely knew was coming).
Also to his credit -- see the quote above about the statue. He pretty clearly wasn't putting himself in the position of "greatest hero on this podium" either; but rather probably shamed that more of his countrymen weren't even taking the smallest steps in the same direction.
-- edit -- I'm not saying he's "not a hero"; I think it's awesome what he did, and I'm not at all sure I'd have had the courage. I'm just adding some context to why saying he was "the biggest hero on the podium" rubs me the wrong way (and it would have rubbed him the wrong way as well).