To argue with a person who ...

To argue with a person who has renounced the use of reason is like administering medicine to the dead.
To argue with a person who has renounced the use of reason is like administering medicine to the dead.

Quotes from the same author

A long habit of not thinking a thing wrong gives it a superficial appearance of being right.
The World is my country, all mankind are my brethren, and to do good is my religion.
The most formidable weapon against errors of every kind is reason.
Arms, like laws, discourage and keep the invader and plunderer in awe and preserve order.
The balance of power is the scale of peace. The same balance would be preserved were all the world not destitute of arms, for all would be alike; but since some will not, others dare not lay them aside ... Horrid mischief would ensue were one half the world deprived of the use of them ... the weak will become prey to the strong.