Spare fuel
As far as I am aware, all airlines comply with reserve fuel policies compliant with their Airworthiness Authorities rules. The purpose of these reserves is to cover normal operation and most of the exceptional cases. It is generally considered to be the pilot's responsibility to identify if "actual" conditions will lead to exceedence of this exceptional case.
What I hope is being suggested here is additional fuel above these reserves without a clearly identified justification. Risk management is imperative, personal margins in the pocket are not productive.
It is difficult to criticise when you have followed the rules to the letter. We are in this business together.