Pilot reported issues with scheduling relating to fatigue and overwork by the company.

Narrative

I am writing about the scheduled; long 10-; 11-; and 12-hour duty days. There are more 3-; 4-; and 5- leg days than ever before. It appears that the Company is solving the staffing and flight-schedule issues by cramming more flights into each duty day; while scheduling more 11-hour days than I've ever seen. This causes massive fatigue and introduces unacceptable risk into our flight operations.My specific concern is making fatigue-related mistakes in the flight deck. I should not be scheduled for any more than an 8-hour duty day. It is unreasonable to be on duty for 9; 10; 11; 12; or 13 hours; operating 3 or 4 legs. Office workers do not work this much in their static environment; and Pilots should not work this long in our dynamic environment. Even with a scheduled 8-hour day; our poor operational performance usually causes that to become 9; 10; and 11 hours.I'm not the only one that thinks this. A recent Captain wrote on a forum; '[A recent Company communication indicates] 'we're at healthy staffing levels!' Does this mean I can look forward to 11-hour overnights and 11-hour duty days for the rest of my career? If I sound grumpy; I may be a little fatigued. 32 hours of duty in the last three days.' I read similar comments on the [forum]; citing excessively-long scheduled duty days; short hotel rest; excessive reroutes; absence of crew meals; and inability to get food and exercise.When I get to the 8-hour mark after three legs; late at night; I absolutely dread the next three hours and the next flight. I have trouble concentrating. I get 'surprised' by things that wouldn't normally catch me off guard. I make mistakes. This is not the result of inadequate rest the night before; or a commute-in. This is the result of expecting real Humans to perform at top performance beyond actual human limits.