I guess it does boil down to upbringing and how one's parents have taught them to behave and interact around others. Not everyone will shun that child. There will be people who treat him fairly, and normally as if nothing is wrong.
Depends on people. But pakistani and infact Asian community as a whole has this dilemma. It's a cultural thing i suppose. We don't expect families to break up. We think a broken family is a dysfunctional family and every member of it is as guilty as each of them.
I hope that made sense.
The child should be treated with equally as his counterparts. The problem happens not so much because we think a every member is as dysfunctional but because when it comes to marriage, people think ("his father thought it was alright to screw women out of marriage, what if the child thinks it's normal too- I don't want my son/daughter to marry a person that will cheat on my kid and break his/her heart") Even though the iilegimitate child could be the perfect Muslim- Many desi don't like taking risk, especially in matters of marriage.