"I'll pray for you" is a Christian's defense mechanism. It is an assertion that the person addressed is comprehended in the belief system of that Christian. It is often a rejection of the nonbeliever's assertion that the entire belief system is a fantasy. To the extent the Christian is referencing "pray for them which despitefully use you" (Matthew 5:44), his assertion of compassion is an insult to the nonbeliever.
But replace the Christian's ritualized hypocrisy with a brain for a moment. He will instantly know that the word blasphemy is defined as "the act of insulting or claiming the attributes of deity." And he will know that the word pray means to ask or supplicate, and that supplicate means to ask urgently, or beg. Celebrating his new-found cerebral power, he will apply the word pray to his notion of deity and discover that pasting the two together will inevitably produce blasphemy. He claims to believe in a deity that is omniscient and omnipotent, one possessing ultimate wisdom and power. He cannot commune, negotiate, manipulate, persuade, coerce, or otherwise induce his deity to treat his nonbelieving acquaintances differently, without indicating to that deity that he knows better than the deity what should be done with that nonbeliever. Doing that, he commits blasphemy.
Suddenly the Christian will find that he cannot pray even for himself, much less for a nonbeliever. His options are reduced to taking voice and harp lessons, in preparation for billions and billions of years of cloudwork. Non-directional mystical meditation, formerly known as omphaloskepsis, or navel-gazing, becomes the Christian's fall-back or default system when he finally realizes his deity construct is about as real as Mother Goose or Father Time.