> Should we have prevented Amazon from investing into AWS?

It's not about preventing it outright. It's about constrain resources to bias towards the invested-in company actually being profitable to allow other companies to compete with them on a level playing field.

> If this was investor funded couldn't Mark fund this himself?

If Facebook didn't make as much money then Mark wouldn't have as much money to invest. Which IMO would be a good thing as it would mean that wealth would be more distributed which would likely lead to it being used more wisely due to the wisdom of the crowd. Mark could probably still launch such a project (and I have no problem with that), just not with "hiring 10,000 staff in Europe for an unproven project" level of resources (which I do have a problem with).