That entire line of reasoning only works if the person you're talking to already considers meat consumption to be inherently cruel.
While those people certainly exist, trying to convince them to be vegan is a form of, "Preaching to the choir.
I've never seen accusations of cruelty change anyone's behavior. I've personally gotten many people to reduce their meat consumption through dialog (and cooking *).
Look up the guy who is generally credited with convincing the most KKK members to quit the Klan and how he did it.