There are several threats to the crypto community, including Bitcoin & Altcoins:
+ Regulations of countries: if countries prohibit crypto mining in any form, prohibit the use or trading of cryptocurrencies, prohibit crypto exchanges from operating in that country, crypto will be heavily affected;
+ Sell-off: if Satoshi, Ripple or DOGE whales do this, the crypto market will be in turmoil;
+ POW miners revolt: this threat existed during the event that Ethereum miners wanted to oppose EIP-1559;
+ The attacks of hackers on crypto exchanges or lending platforms…;
+ Quantum computing: crypto isn't ready for this yet. Currently, as far as I know, only IOTA's Tangle technology has an effective solution against the attack of the quantum computer.