I flew longhaul from 1997 to 2013. Tiredness was a constant - especially when flying and home life were added together.
Fatigue is far more dangerous in that you don't realise how badly you are performing - I think the effects of alcohol are very similar so VS
need to take their crews concerns seriously.
All airline crew are humans first and foremost and even if a computerised scheduling tool says it's legal safe to fly the results - over time - will lead to mistakes and thus potential accidents.
For passengers - take a look at your crew boarding at their home base. If they are showing signs of "tiredness" after being at home then that could be fatigue....