The answer I see to this is that Arrington is rewarded because he is making the investments on behalf of the investors. I would hazard a guess that many of the people investing in Arrington's fund made their money outside of tech, and therefore do not possess the skill set to critically analyze tech investments. But they know the technology sector is a good place to invest, so they hand their money to someone with the proper skill set to invest in it. In this case, that person is Arrington.
He is rewarded because were it not for him, the people investing in his fund would be unable to intelligently invest in the tech sector.
Another question you have to ask - if his income was subject to income tax versus a LTCG tax that's currently in place, would he stop doing what he does? Reading his original post, most likely not. Maybe he'd raise a larger fund next time to justify the 2/20 fee structure, maybe the structure will be changed to 5/20, but investors will still chase the yield, and there will be someone on the receiving end happy to accept investors' money.
Remember, carried interest is different than capital gains, which would suit your argument better.