First of all, if someone was expected to something (it doesn't even matter why he has expected it) and he got something different - he's disappointed. He came here and share his disappointment, I can't understand what's wrong with that or how is that "bitching".Secondly sometimes people are impulsive and they're just saying what they think at the moment - some of them are even going to change their opinion after hours, days, weeks or months - but you can't put logic over people feelings. And feelings definitely doesn't "comes up with reasonable arguments" like you said.
Not everybody are musically educated, some people just divide their music by "I like it", "I don't like it" and "it's ok", and nothing is wrong with that.
Exactly, the band changed their style, but you read the same complains, why? Because LP has so many genres and combinations in their songs, so the people who are listening to LP are very different from each other.Some listening to metal, some to mainstream rock, some like nu-metal, some like rap and hip-hop and some like electronic music. Everyone wants the band to pull it a little bit to his "side", I'm totally agree that no one should say what kind of music the band should play, but it's understandable why they want it or think like that.
Everytime that the band released a new album, the reactions were splitted to three or four groups, nothing shouldn't be different this time.