The safety net is the Captain, but remember by definition a net is full off holes. Catch even the best/most experienced on a bad day, fatigued, under threat of redundancy, terrible weather etc... and you could be looking at things going bad very quickly. The First Officer is equally the safety net, he also needs to be able to recognise an impending situation, flawed decision making model and say "respectfully, what the f#$k are you doing Captain." That is where filling the RHS with inexperienced bods will fall down.....and fall down it will
It's a two way street. The Captain is ultimately responsible but he needs to have confidence in/trust his oppo. (right hand man/woman).