18th-century people did not use so-called gender-neutral language

Pet peeve time.

If you quote an historical figure you admire, but you change the wording in order not to offend modern ears, then what you have is not a quotation but a paraphrase, and it should be labeled as such and should not be put in quotation marks.

I see this frequently where "man" is changed to "person". The most recent example is a shortened version of a quotation from Thomas Paine that's making the rounds on Facebook.

The Facebook version:

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

Here's what Paine actually said:

“To argue with a man who has renounced the use and authority of reason, and whose philosophy consists in holding humanity in contempt, is like administering medicine to the dead, or endeavoring to convert an atheist by scripture.”

If you really admire the person, then show him or her appropriate respect and leave the original words intact.