Well, really Meyer wasn’t the first to allow vampires a soul. Angel and Spike from Buffy both had souls, which they had to work very hard to get.
I’m sure the people who hate Twilight so much, also Hate Buffy the Vampire Slayer, the movie/tv show/comic book.
Maybe the Cullens are like Angel and Spike and are working very hard to get a soul back. They don’t know whether they have a soul or not, so they still choose to be good just in case, which is very painful for them. Angel had a soul, then it was taken, and then he got it back. Spike wanted to be good, so buffy would love him, so he went and got his soul back from the beyond.
Stephenie is not the only writer to put souls into vampires, Joss Whedon did it also. She’s also not the only one who said that vampires and humans could create babies, that is a very old legend.