More Severe than the Three Cardinal Sins:
The Chida zt”l (Sefer Lev Dovid) quotes Sefer Birchas Tov as saying that lashon hara is the very worst aveirah. It is even more severe than the three cardinal sins of idol worship, immoral relationships and murder. Therefore, the current golus, which was caused by lashon hara, is longer and more difficult than the previous golus, which was caused by those three sins.