Whether one should invest in bitcoin or not depends on whether you think Bitcoin will become a long-term trusted store of value.
If it does become a long-term trusted store of value, BTC should trade around $2,000,000 a coin (depending on how many coins are lost and are actually in circulation). That is over 100x the price of where BTC is today.
If BTC does not become a long-term trusted store of value, its likely price will be close to zero (unless it becomes a "cool" collectible... which is a possibility).
So if you think BTC has a 10% chance of becoming a long-term trusted store of value, it is a good investment with a nice expected return. It is still very risky but professional investors should invest some small portion of their portfolio in this case.
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If you think BTC has a 1% chance of becoming a long-term trusted store of value, you should not invest.
If you think BTC has a 0.001% chance of becoming a long-term trusted store of value, you might consider a short. 