Let me explain why I hate that phrase. Having been at the receiving end of it my entire life, I have found that it is generally used as a sort of disguised insult. The people who use it in such a way intend for you to perceive it as well-meaning (and, in fact, and number of them may genuinely use it for a good cause) however, it is almost always used the same manner that you might tell someone, "You need to get an education." Well-meaning, but ultimately in bad taste.
It assumes that the person being talked to is either inferior or somehow lacking a desired quality. In the same way that you might believe a person is lacking intelligence, these people (scornfully, perhaps) believe that a person is lacking their god's blessing or lacking god altogether.
Sometimes the word is even used in obvious disdain and pity. Having been raised Jewish, I am very familiar with the experience of telling people that I wouldn't have a merry Christmas because I would be celebrating Chanukah instead, only to meet the reply, "Oh...well God bless you as you descend into Hell" (If only I had the presence of mind to inform them that only Christians go to hell, us Jews don't believe in it
). Then there are the times when Christians, shocked at the fact that we Jews really
don't hide horns under our curly hair, would utter "God bless you" just as they turned their back on us to walk away.
Those are extreme examples of very misguided people, but I'm sure they serve their purpose of illustrating the lengths people will go to as they insult you using something that, I believe, was intended for a much greater cause.
Unless I'm sick or starting out on a long journey, I don't ever want to hear those words. So I heartily say, "God bless you" to everyone who inappropriately uses that phrase. God knows you'll need it.