On the contrary, it seems more likely that Musk would've not only thought about risks already for more than a couple hours, but that he would've consulted a lot of domain experts about such things before even deciding to take on such a project. Even the most optimistic business person isn't naive enough to take on something they see as a sure bet to fail. Not to suggest that there haven't been entrepreneurs attempting silly businesses before, but rather that one should pause and think about the possibilities of how something might work, before jumping to the conclusion that they already understand everything there is to know about a project, and that it definitely won't work.
As another comment mentioned elsewhere in this thread, a good entrepreneur's main skill is being able to figure out some unique/unorthodox way to make something work, and capitalizing on that. Now, that doesn't mean that everyone opposing these ideas are wrong or don't know what they're talking about, it just goes to show that a lot of people's default state is one of risk-aversion.