Mistakes happen. People forget which environment they are on. people forget where statement in their DELETE query. People misremember their cwd prior to running rm. Sometimes it's lack of experience, sometimes lack of sleep, sometimes just shit luck. Very rarely it's lack of responsibility.

And regarding your team members: if you don't trust them, don't rant about it on public forum, man, move them away from important systems, implement personal improvement plan, and when that fails, fire them.