Why is P2P insecure?

I understand that Peer-to-Peer (P2P) networks have been gaining popularity in recent years, particularly in the realm of cryptocurrency and file sharing. However, I'm curious about the security concerns that often surround P2P networks. Can you explain why P2P is often considered insecure, and what are some of the specific vulnerabilities that make it a target for hackers and other malicious actors? Additionally, what measures can be taken to mitigate these risks and enhance the security of P2P networks?