In this article the father was upset that the teacher had sent an email. In my opinion, I really don't see a problem with this. If the email was between the teacher and the parent, no one else would know. The only reason everyone found out is because the father made the email public.
I used to send emails to parents when I had concerns about their child, although I never has a situation as severe as this. In my case, I wanted the parent to be aware of what was going on in class. Phone calls from my classroom were never private because there were always students in my room. Mailing letters to the child's home can work, but the parent may not receive them for three or four days. By that time, the situation with the student could have erupted into something disastrous. There's also a chance that the child will intercept the letter before the parents see it.
Telling the principal and counselors also works, but again, getting everyone together for a conference can take a couple of days.
If a teacher wants to let a parent know about a potential situation and wants to let them know quickly and privately, I think an email works perfectly. The other reason I liked email is that I always had a record on my computer of any correspondence. I kept an email folder of such messages so that I could always document actions I had taken to remedy situations.
In this situation I think that the parent, upon receiving the email, should have immediately called the school to set up a conference with counselors, administrators, teachers, and the student. Instead of complaining about the teacher's emails, the parents should be taking action to help their child succeed in school, in life, and help the child's teachers feel safe.