The implication is that these people's opinions of themselves are unwarranted by their actual accomplishments. It should be an easy test: how many TED speakers have followed through and implemented their ideas?

This is an incorrect rubric to judge the quality of these talks. The implication of your statement is that there is no value in speaking on current research or ideas until some point where the technique has been realized. But this misses the importance of spreading ideas for their own sake, to get people thinking about and excited about the future that technology can bring us.

TED seems to be a "futurology" organization in that it offers a glimpse into a future made possible by technology. They make no apologies for offering a positive outlook on the direction technology and society is moving, and I'm perfectly fine with that. There is a counter-movement to ramp down on positivity as if somehow we are better served by a sober analysis, and that anything more is naive or religious dogma in disguise. This not the case.

I'm not implying anything - just explaining why "arrogance" is considered a negative. Someone is not called "arrogant" if they have actually delivered on what they claimed. Usually, it's applied to people who brag without anything to show for it.

I would disagree with the claim that successful people aren't called arrogant, and that its only applies to people who "brag without anything to show for it". I've seen many instances that contradict these points. There is something more going on beneath the surface here. My guess is that there is a psychological need to tear down those out there busting their ass to accomplish their vision. It's just disappointing to see that coming from this group.