It isn't a matter of not tolerating imperfection, it's mostly about hyperbole (which the OP ironically displays itself). I don't have an issue with players' form being criticised if they aren't playing well, especially if people have the nous to pick out parts of their game that need improvement. The problem is when people start making ludicrously negative statements ("they're finished", "they don't care about the team", "they're League One standard", etc.) about our players in general that are both pejorative and completely out of sync with reality. The players from the 2013-14 vintage in particular have had extremely negative things said about them on here out of all proportion to their quality as players.
The other thing is that because fans have favourites, certain kinds of players tend to be favoured above others if not outright untouchable at times, until they suddenly aren't. If someone's tall, German and has hair you could toss one off in the shower to, they can do no wrong for months, right up until their performances reach a critical mass of disappointing at which point they're shit and in fact have never been any good. If you want to talk about Coutinho, he's long had issues with consistency, especially with regard to end product, and could contribute a lot more within the game a lot of the time. That doesn't negate what's good and often great about him, but pointing out those issues is fair.