Who or that

Do you say "who"? Few do, as "that" replaces the personal pronouns "who" and "whom". "Whom" has been too hard for most English speakers for a long time, but why has it become so hard to use "who" when you're talking about a person or people rather than "that"?

The girls that sang, the boy that cried wolf, she that must be obeyed, etc I find wrong and ugly, but what do you think?

Ted, i think when we talk about THINGs ,should use THAT , as i did.
For other points can use WHo.This is the best way for recognize them,i think,Goodluck.

I always use try to use who or whom for people, and which for things, although in speech sometimes "that" instead of "which" and "who" instead of "whom".