In all likelihood, anything that exposes your email address to public access will cause you to receive increasingly more and more spam and phishing attempts. Even if your email address is secure, hackers may be able to uncover the IP address linked to the address and use that information to target you with other attacks.
Whenever you want to give your email address to someone on an Internet forum or another type of online discussion site, it's best to do it privately, via a private messages. In addition, if you type the address out without the "@" and "." symbols, you might be able to protect your email from being captured by automatic scanners and bots.
Most attacks aren't very sophisticated, though depending on the type of person you're receiving spam emails or misleading information could potentially compromise your security. Though, I think most people with common sense know the telltale signs these days, and the users that would fall for this type of spam, would likely be compromised in another way even if they didn't expose their email address.
Email addresses were made to send, and receive information over the internet, so yeah email addresses were actually designed to be revealed to other people. Of course, if you care about privacy, and not exposing your email to every Tom, Dick, and Harry it's probably best to hide it.
I do agree with your last statement though, emails were originally designed to be shared among friends, obviously with how things have progressed with the internet, they've become so much more than that, and therefore its common these days to put your email on your website etc.