Truth hurts
Yup.
"But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed. As we said before, so say I now again, if any man preach any other gospel unto you than that ye have received, let him be accursed." - Galatians 1:8-9
And that includes Mohammed, who certainly preached a different gospel than Jesus did. If the muslims have a problem with this cartoon, then they also have a problem with Saint Paul.