I'm no expert, so correct me if my thinking is way off on this. But look, some people are comparing Bitcoin alone or Bitcoin and other alts with the Tech bubble of the 2000s. If Bitcoin and/or cryptocurrencies represent Internet 2.0 or 3.0, and not only that, but is a currency and a store of value - something that has the potential of changing not only how we use the Internet, but also how we do transactions and store value - you can't even compare it to tech/IT stocks in the early 2000s.
The 280 dot.com stocks in in Bloomberg US Internet index had a market cap at $3 trillion in 2000 before falling down.
What is the market cap of Bitcoin? $52 billion. Total crypto currency market? $107 billion.
So in order to even compare it to the dot.com bubble we need the entire crypto market to 30x. Could Bitcoin be in a bubble at $90,000 USD per coin? Sure. Would I care if it fell from 90,000USD to 45,000USD? Of course not.
I strongly believe that even if my heart jumped a little seeing prices above $3000 today, these prices are ridiculous.
Who knows if we can really compare the whole crypto-market to the whole IT-sector in 2000. But maybe right? The world is also bigger, more people are in position to invest. The crypto-currency market is world wide. We're billions of more people today than in 2000. More people are out of poverty and countries like India, China and others are in the game.
All I know is that we should be cautious about screaming bubble and comparing it to the dot.com age. Sure, bubbles exist and Bitcoin will have small and big bubbles.
At a minimum I don't smell bubble before $10,000 USD. At that point I will sell about 10% of my Bitcoins to hedge. At that point I would have 10x'ed my initial investment in Bitcoin, and selling 10% at that point is reasonable in my opinion. But selling anything before that point doesn't really make any sense if you're long term and believe in Bitcoin.
(This is not professional advice, merely my personal opinion. Du your own due diligence)