The two are not mutually exclusive (having merit, and being promoted out of a desire to be more diverse and inclusive). For something like Techcrunch Disrupt, being diverse - whether about race, gender, type of ideas, geography, social background - is reasonable and valuable, because it gives a greater chance of serving a range of purposes from providing role models to giving valuable insight of issues unique to whatever background the person in question brings to the table.
Promoting diverse individuals who merit promotion is great. Promoting diverse individuals who do not merit promotion is harmful to the diverse individuals who do merit promotion because people will assume that they're being promoted for diversity instead of merit. That is a very bad thing and worth criticizing. Again, Arrington didn't actually do this since the person in question is objectively impressive, but saying that he would promote someone for diversity's sake is unquestionably bad.
The purpose of putting people on stage is not always to showcase just the best, but often to showcase different viewpoints and different ideas.
Promoting just the "best" from the viewpoint of a single background - now that is arrogant and harmful because it assumes you actually know best. If Mike always knew who was best to promote, he'd be a billionaire and every company he invested on would have people everywhere throwing money at them.
As such, especially for something like Techcrunch Disrupt, it is valuable to promote a diverse group - whether based on race, socioeconomics, geography, gender - especially if a group is severely underrepresented - to get a wider view and perhaps learn something from it.
If anything, a great deal of hidden racism is a direct result of people insisting on picking what they think is "best" without taking into account the hidden biases brought by their upbringing, school background etc. and never being exposed to a more diverse set of views.
I buy that argument for a conference of ideas, but not for a business competition. The former is about exposing people to new ideas; the latter is about exposing promising companies and investors to each other. Getting people with diverse backgrounds to speak at a conference of ideas is doing the audience a favor, but this whole conversation has been about doing underrepresented minorities a favor.
Promoting underrepresented minorities based on their status does not help underrepresented minorities. It hurts. It might help the people who are blessed to be in their presence, but the assumption of pro-minority bias makes people think less of minorities when that becomes a common practice. It should be discouraged.
It's a bizarre thing to criticize.