Explain the meaning of "The moral barriers that I had supposed to exist between me and the dangers of a criminal career were so tenuous as to be merely non-existent"

"The moral barriers" as in ethics and morals, "that I had supposed to exist between me and the dangers of a criminal career" as in morals that the character put into place about how dangerous being a criminal could be "were so tenuous as to be merely non-existent" didn't matter to the character.