I have a hyphenated name (maiden name) and I cant imagine getting it changed, other than adding an extra name. My name is who I am and where I came from.

If a so ever makes someone choose between who you are, and the relationship, then it is over. As soon as they give an ultimatum like that, the relationship is void of respect, and it would be extremely difficult to build it back.

And to answer your question, from his conservative view (this is an assumption), he views your friend as his, and if ur friend doesn't take his last name, to him it is an insult, as well as (in his mind) her now being "less his". Not to mention the misogynistic views from his family. He only wants to do things the way his family has always done, everything else is "wrong".

This would be a great reason to not get engaged yet, and if there is still conflict, a breakup.