Booker T. Washington had a very good reason to argue against the slave system, he himself had a first hand experience in it as a slave.
The slaves were not taught how to value property, because they did not own any, not caring for it as an owner would, letting it get run down. Once the slaves were free they had to learn how to be responsible for themselves and learn how to make their own decisions, without anyone telling them what to do very much unlike their previous lifestyle. Their lack of education was extreme! They weren’t taught how care for their health sufficiently, most living a filthy mannerless life. There also was no marriage system, therefore most children didn’t even know who their father was!
If the slaves had been taught just a few of these things they would have had a huge head start once they were free but, unfortunately they had to learn these lessons the hard way, by being pushed straight into the real world.