Bitcoin has a strong base of advocacy not based on any logic or utility but solely sprung from the mule stubbornness of those who profited from their speculation.
1. Bitcoin is environmentally damaging. It produces 37 megatons of CO2 per year and consumes 78 terawatt-hours of electricity annually. Much of that electric consumption is powered by coal. Not all energy consumption or CO2 output is bad, but value should be provided commensurately to society for the damage incurred. And yet:
2. It is a terrible currency. Promoters claimed we could pay for things with Bitcoin, that it'd replace fiat currency. But the design of Bitcoin in particular makes it an awful currency. To prevent deflation, a currency should be able to increase its supply to maintain reasonably constant velocity as demand increases for it as a medium of exchange. With its limited number of coins, Bitcoin cannot increase supply to maintain velocity: its only solution is to fractionalize, a form of deflation. And deflation is what we get. Massively: everything you own, and all your income, constantly becomes worth less expressed in Bitcoin, day after day.
3. It's a terrible currency, part two: currencies should have very low transaction costs. Bitcoin transaction costs exceed $20. The response to this is to recentralize it in the form of services that cheaply transact Bitcoin rights management through traditional databases. Eliminating the very value proposition of Bitcoin.
4. After having given up on defending it as a currency, the next claim is that it's a "store of value." But stores of value should have some degree of consistency of value: volatility is not a virtue. Bitcoin supporters are right that fiat currency, to the degree it is exposed to inflation, is at risk of not being the best store of value, which is why we don't normally keep huge amounts of resources piled up as cash. But Bitcoin is an awful store of value because it has no fundamental utility that moderates its price swings. Normal assets - real estate, bonds, gold - have some sort of fundamental utility or cash flow that helps to moderate price action over time. The asset must have some sort of use first, then it can become a good store of value. Because of the above flaws, Bitcoin has no good use, which thusly makes it a poor store of value.
None of this is a fundamental problem of crypto, just Bitcoin. Crypto could be very useful! But with many millionaires minted from a lucky speculation and their entire ego reliant on deceiving themselves that their speculation was clairvoyance, critiques of Bitcoin are invariably met with a flea market of intellectually mangy defenses that ultimately boil down to saying "well, look at its price!"