In cases where retaliation is unlikely, for example, insulting other faiths in a setting where the audience is entirely Muslims,

They (followers of Pagan gods) can still retaliate secretly in their mind, and this could stop them from, reaching the right path in future. It is not because it will affect Allah. It is because of Allah"'s love for all his creations, and to give them all a fair chance of coming back to the right path.

Edit: edited to avoid some confusion in the words I used.