I tend not to intervene. I did it once when an unsufferable passenger in row 1 who had been moaning from the start and complaining about everything told the flight attendant that 'nowadays, FAs are only good to mop the floor' at which point I told her that whatever bad experience she had had, that was enough and that there was no excuse to be rude and personal and that I'd give the FA my contact details if they wanted to file a complaint and needed a witness. It calmed her down and the FAs seemed relieved as they had tried many different things to calm her down already!

That said, I do make some allowances for people being abnoxious when things go wrong. I sympathise with the OP's wisdom but by experience I know that some people find it hard to take when things go wrong especially as you never know what the consequences are for them.