WrongBot:

The "deep moral dimension" generally applies to group memberships that aren't (perceived to be) chosen: sex, gender, race, class, sexual orientation, religion to a lesser extent.

This is not an accurate description of the present situation. To take the most blatant example, every country discriminates between its own citizens and foreigners, and also between foreigners from different countries (some can visit freely, while others need hard to get visas). This state of affairs is considered completely normal and uncontroversial, even though it involves a tremendous amount of discrimination based on group memberships that are a mere accident of birth.

Thus, there are clearly some additional factors involved in the moralization of other forms of discrimination, and the fascinating question is what exactly they are. The question is especially puzzling considering that religion is, in most cases, much easier to change than nationality, and yet the former makes your above list, while the latter doesn't -- so the story about choice vs. accident of birth definitely doesn't hold water.

I'm also puzzled by your mention of class. Discrimination by class is definitely not a morally sensitive issue nowadays the way sex or race is. On the contrary, success in life is nowadays measured mostly by one's ability to distance and insulate oneself from the lower classes by being able to afford living in low-class-free neighborhoods and joining higher social circles. Even when it comes to you personally, I can't imagine that you would have exactly the same reaction when approached by a homeless panhandler and by someone decent-looking.