How safe is proof-of-stake?

As a professional practitioner in the field of cryptocurrency and finance, I often encounter inquiries regarding the safety of various consensus mechanisms. Among them, proof-of-stake (PoS) has garnered significant attention. However, the question remains: How safe is proof-of-stake really? On the surface, PoS seems promising, as it relies on validators staking their coins as collateral, thus incentivizing honest behavior. This approach theoretically reduces the risk of malicious attacks, as validators have a financial stake in maintaining the integrity of the network. However, are these safeguards sufficient? Concerns have been raised about the potential for validators to collude, forming cartels that could manipulate the network. Furthermore, with the stakes being held in digital form, are there adequate measures to protect against hacks or exploits that could compromise these funds? In essence, while PoS appears to be a step forward in terms of security, there are still lingering doubts about its overall safety and resilience. As a professional, I believe it's crucial to thoroughly understand and evaluate these concerns before drawing any conclusions about the safety of proof-of-stake.