The video is a little over 2 minutes long, and your takeaway...

The video is a little over 2 minutes long, and your takeaway from this is "we need more carbon"?
Did you just ignore everything else?

Regardless if Elon Musk is for or against tackling climate change, he is an engineer not a climate scientist. (Which by the way, one of Elon's goals include reducing global warming via sustainable energy. Why do you think Tesla even exists?)
It's no different than Al Gore's, Donald Trump or Mel Gibson's opinion on climate change. Science is not dictated by celebrities.

"Carbon (dioxide) in the atmosphere would cool the planet".
No.

The only place in the world which is cooled by Carbon Dioxide is Antarctica (and occasionally greenland). You are misrepresenting the argument that one place on earth is cooler therefore the planet will be cooler. The entire Earth on average is heating from Carbon Dioxide, not cooling. (additional source on how this cooling affect works in Antarctica is here)
Supporting image from the sources to show that cooling does happen with increased CO2 (but of course with way more heating)


If you want to make a claim that Carbon Dioxide is cooling the planet, you're going to need some serious sources for this.

Greenhouse gasses are made up about 80% carbon dioxide. In fact, the word "greenhouse gas" should be a very very big hint to why CO2 does not cool the planet.