So far,Mr.Burchell has seemed friendly but with the discovery of the letter assumed to be about the Primrose girls,he's become Public Enemy #1 overnight. I'm not so sure that his intentions were all that dishonorable. To start off with,the letter itself:

“Ladies,

“The bearer will sufficiently satisfy you as to the person from whom this comes: one at least the friend of innocence, and ready to prevent its being seduced. I am informed for a truth, that you have some intention of bringing two young ladies to town, whom I have some knowledge of, under the character of companions. As I would neither have simplicity imposed upon, nor virtue contaminated, I must offer it as my opinion that the impropriety of such a step will be attended with dangerous consequences. It has never been my way to treat the infamous or the lewd with severity; nor should I now have taken this method of explaining myself, or reproving folly, did it not aim at guilt. Take, therefore, the admonition of a friend, and seriously reflect on the consequences of introducing infamy and vice into retreats where peace and innocence have hitherto resided.”

The letter is not signed and even tho,Mr.Burchell says he is the author,that may not be the case. He might've just said out of anger at the vicar for reading it without permission. Also,the letter is rather vague,IMO,about who is really being warned-the "impropreity" may not really be about the character of Olivia and Sophia but rather what they may be exposed to by going to town and who might have more access(yes,I mean Thornhill)to them.