According to Ariz"l and his followers, the sequence of Yaacov's marriages (Rachel first and then Leah) was of a great importance, dealing with the Seider of the Geulah, Moshiachs etc. Lavan planned to undermine that and harm the Jewish nation for generations (hence the everlasting fights between the Tribes, for example).
Rachel and Leah are presented throughout all interpretors and Midrashim as Zadkaniot and having Ruach haKoydesh. However in fact, they helped Lavan with his wicked plan, and, therefore, deeply betrayed Yaacov.
How could they switch sides?