That was the point, to paint the Godfather as a sympathetic character, who only killed people who needed killing, not as some raving bloodthirsty madman.
Bingo! The family used people’s vices as a means of income; they were going to drink or gamble anyway.
The Solazzo thing with drugs turned off Don Corleone who saw it as a different means of corruption. That went against the younger, greedier Dons who didn’t emigrate here and go through the hardships he did as a young man. That is why they tried to bump him off and lead to “the mattresses.”
The book was very controversial because it did portray gangsters in a positive light.
My freshman year in college, my roommate found out that I didn't know about page 28 of "The Godfather". She gave me a copy for Christmas and I stay up all night reading the book because it was so believable. and well written.
Well, I thought it was, anyway.