Guys, there's a very good in-the-real-world reason why Rey shouldn't fall to the dark side, which is that as the first high profile (higher profile than Ahsoka, since this is a movie and not a tv show) female Jedi protagonist in the franchise, she embodies the hopes and dreams of a lot of the female fanbase and a potential new generation of female fans, and to turn her evil will ruin a lot of that. Male characters are taken as the default, so we as men don't really care when a male character turns bad or has to be redeemed by others; but since there are so few role models for young girls to cling to in the films in comparison to the amount that guys can, Rey is a disproportionately important figure right now.