Here's the gist: it's not that posting an opinion online is hubris, it's what your opinion entails and is based on. You have no facts about the deal, and no qualifications to speak on good business acquisitions. You call the product "worthless" while teams of people at Facebook and Google seem to value it very highly. I'm going to have to assume that the people FB and Google hire are all very intelligent and capable at their jobs, and they see value in purchasing the company (which is why they made the offer). You, however, with no information have decided they're all morons and you know better because SnapChat is "worthless". That, my friend, is indeed hubris. You assume that you know more than everyone else who has far more intimate knowledge of the company and product.
Here's the moral of the story: just because something seems "worthless" to you doesn't mean that it has no worth to anyone else. If other highly trained and educated people say it's worth quite a bit of money, then, perhaps, you should re-evaluate your viewpoint.
Or if he did sell and used the money to go on a cocaine bender and died in a hotel pool from an overdose - would selling have been the best thing for him?
Do you see how pointless "what if" scenarios actually are? There are too many variables to properly account for - you can't just change one variable (like a decision) and assume everything else turns out exactly as you would like.
Also, just because someone makes a decision that's different from the decision you would have made doesn't mean their decision was the "wrong" decision. You would have taken the money, I would have taken the money, and I'm sure a lot of others would have taken the money. However, choosing not to take the money isn't the "wrong" choice, it's just a different choice. And, given that he had all the information about the deal (or at the very least more information than the rest of us), I'd say calling his decision wrong when you hardly have any information on it at all is its own form hypocritical hubris.
Anyway, morals of the story are (1) different !== wrong and (2) it's best not to judge the actions of others, especially when you're lacking the details.
PS. I am so judging you.
PPS. I am also fine with being a hypocrite.