True, there are some crap companies in there, but how do you see those in advance? Uber and Tesla aren't the best run companies, but they each have a great concept/products that their customers really like. Great concept/products that their customers love would describe Amazon and Apple 10 years ago and look at them now. These companies might tank or they might grow exponentially. Uber, Tesla, and WeWork are also each a tiny <1% fraction of VTSAX so who cares? You are making a microscopic bet in a few companies you wouldn't put real money into.
What we do know: Most active strategies underperform VTSAX over time. That was probably too conservative. Let me rephrase that, 85-94% of active strategies underperform VTSAX over 10 year periods*. If we stretch it to 40 year periods only 5, out of thousands of active funds, managed to outperform the Vanguard 500 index**. This is the reason funds like this are becoming so popular and it's the reason people like MMM recommend them. Is it perfect? No, but it's darn close and it's reliable that it will stay that way. Some people will do better, but most of the people 'trying' to do better will end up doing a lot worse and paying excessive fees in the process.
*Source: Vangaurd's regular Performance reports showing how their index funds did against their active peers. I've seen the % as low as 85% and as high as 94% for 10 year periods.
**Source: The Little Book of Common Sense investing (J. Bogle)
That all said, I don't think someone should only be in VTSAX. VTSAX is a great way to get your US stock exposure, but you should diversify across asset classes, for instance adding international, bonds, real estate, etc.