“Thanks, but I find that quite horrific.”
Think! They have no way of knowing who is on the line. It could be a friend that the prisoner is wanting the friend to whack a witness.
That would be very easy to handle. When you want to phone/contact your lawyer personnel from the jail set up the connection. And, yes, I have heard about corrupt lawyers, but how about “innocent until proven guilty”? (In this case the lawyer, not the convict waiting for sentencing.)