“They sent a few emails soliciting donations” isn’t exactly a horror story in my experience. Seems hardly worth mentioning!

It's not something to stop using them over, but unsolicited solicitation emails are annoying at the least. It's definitely worth mentioning letting other people know they have warts too

To be clear, I was merely answering the question posed "has anyone actually commented to you in a negative way about using Let's Encrypt?"

Well, yes, someone actually commented to me in a negative way about using Let's Encrypt ....

Don't shoot the messenger, as they say.