What bad behavior did Rousseau learn from his apprenticeship with M. Ducommun; what is Rousseau arguing here?

Abel Ducommun was an engraver in Geneva to whom Rousseau
was apprenticed in 1725. The choice was not a positive one, as the engraver is described
as violent and as incapable of developing a positive relationship with Jean Jacques. He
often punished his apprentice and his violent behavior eventually led Rousseau to escape
from Geneva. Therefore Ducommun was a negative teacher for Jean Jacques as he taught him
to be violent and, with himdsight, the author holds him responsible for his own moral
degradation. The character of Ducommun proves Rousseau's ideas on the corrupting effects
of society: although he is originally from a good family, Ducommun goes through quick
decay and dies in poverty.