What is this new fad of addressing people as hey,  don't they know it's disrespectful and downright discourteous?

I just assume they are Americans from rural areas or the southern or western States. We have "Hey!" sayers in Canada too (or are they "Eh?" sayers?), and I think they are either from the Prairies or from over the border. That's how westerners talk, I suppose; those wide open spaces I suppose (except for Buffalo).

I don't care for the informality either; but you can't teach good manners by telling people you think they are impolite.

It used to be common but it's going out of fad. Not to worry.

I agree.  It seems to be a construct of television.  If someone says "Hey" to me, I generally ignore them.  If they write it, I reply "Straw", or "Barley", or some such thing.  

"Marli" is completely wrong.  I've lived 40 years in Alberta ("the Prairies" to her) & have NEVER heard anyone here address another in that way - or by saying "eh", for that matter.  It's also not said by "Americans" as they're all the people who live in the western hemisphere, from Canada to Argentina.  She further errs to think "you can't teach good manners by telling people you think they are impolite."  Really?  How else do you do it?          

Not at all in my opinion

It is done because their name is not known.

Hey, I completely agree with you. When oh when will they ever learn, etc.

That's a matter of opinion. However, we live in a time where disrespect appears to be more in than respect.

Hey, what the heck are you talking about?

Specifics would be useful here.

they probably know and dont care

Hey, no it's fine homie.