This fear is legitimate but it assumes all PoS protocols slash for each infraction, even if those infractions occurred within close vicinity of one another. Cosmos BPOS at the start on the network only applies a severe slashing condition upon equivocation. So perhaps your validator’s failover proxy goes rogue because you programmed it poorly. Now your backup validator node thinks your primary validator node is down when it really isn’t. Suddenly, you’re double signing. But not because you’re malicious. Cosmos BPOS accounts for mistakes and only slashes you for the first double sign. This prevents the protocol from slashing you to zero.

What I’m saying is: not all PoS protocols with slashing conditions are created equal. Casper is but one example.