It's irrational to believe that you're more likely to be correct in that assessment than any other person who makes a bet on a specific stock.

No, it is not. This is one of the few times you are actually allowed to trade based on insider information.

If you are capable of correctly estimating that, you are likely better off running a hedge fund than working at Google.

Not really. Employees can have much more information and market insight than an external analyst, especially in tech.

Yes, but what you need to be able to predict is how the market is going to value your stock in $N years. Knowing that you have cool tech coming down the line, or that your colleagues are way smarter than your competitors', etc, might give you inside that analysts lack, but it rarely qualifies you to predict how the stock is going to perform - particularly in a large enough company where the pieces you see are small picture relative to the overall performance of the company.

It's also easy to get blinkered, and deceive yourself into thinking that the company will be successful despite the warning signs that those outside the company might see.

I worked at a bank during the GFC. And it was easy to believe (perhaps correctly, but that's irrelevant) that we weren't really in that much trouble. We were solvent, we were diversified, we weren't exposed to sub-prime, etc. But the market took a beating to us. And it didn't feel like that was justified. But that simply didn't matter. The stock was in free fall, and even if we were right and the market was "wrong", the market is always right because that's what sets the value. If you could afford to take a long term view, then the price recovered, and it wasn't the end of the world (though there were definitely better performing investment options). But I had colleagues who were leveraged against company stock and were getting margin calls every second day.

Which brings me to my second reason for hating to hold stock in my employer - those colleagues couldn't sell their stock due to insider trading rules. They had to find the money for the margin call, because the fact that they had "much more information and market insight" (as you put it) actually meant they weren't allowed to sell. Holding (public) stock in your employer is a big risk because even if you see the price crumbling, you may not be able to get out, and you just have to take the hit.