If they're abusing their position they don't deserve to keep their job. The companies complicity makes them party to whatever these staff do. Whether a lawyer can prove that or not depends on the depth of the aggrieveds bank account.
Yes.
Should you have been fired? Depends on how much you abused your privilege and what you did with that information. Your comparison to 1 strike laws and greater crime is pretty rich given the information you improperly accessed could be used to blackmail others, or whatever. It's important to treat such information with the utmost respect. Your cavalier attitude and inability to accept responsibility in this regard may be very common within the tech industry, but such attitudes are also why there is a growing movement to; take data out of the hands of companies, and to harshly punish companies who fail to protect the data on one hand while vacuuming up as much as possible with the other.