Rather than getting defensive in the face of what's a very valid criticism, why don't you work on improving your product?
Being more transparent about the message that you're going to send, as well as adding the ability for the user to edit that message, would help you much more than a half-assed defensive statement on Hacker News ever would.
I'm not being defensive (which I know sounds defensive) I'm just explaining how things actually work. That there is a message, but like many things on the internet people don't always read everything.
The fact that you are acknowledging that "people don't always read everything" makes it very hard to believe this is anything other than an intentionally deceptive pattern. A responsible and ethical UX designer would show the email and allow an easy path to opt-out of emailing anyone.
"but like many things on the internet people don't always read everything."
I agree that many people don't read everything they see on sites, but I believe we should optimize our sites/products for that, to help those people pay attention to the details that matter to them.
It's YOUR responsibility to make sure the user is well aware of the ramifications of what's about to happen.
Not reading the terms and conditions of Reddit when all you do is browse and read and never even log in: not too important.
Not FULLY understanding that you are going to send an email to my contacts, using wording that YOU wrote to make it appear as if I wrote it: pretty damn important.
Being more transparent about the message that you're going to send, as well as adding the ability for the user to edit that message, would help you much more than a half-assed defensive statement on Hacker News ever would.