Hate for Wikipedia comes from a few places.

The first and most important is that most people who have tried to edit Wikipedia have their first edit reverted, usually with good reason, because they don’t understand the procedures and policies. Unfortunately these procedures and policies are what maintains high quality.

Related is news articles and blogs about edit wars and less frequently that an article or group of articles is genuinely captured by one volunteer who will protect their own little fiefdoms and not allow anyone else to edit them. This happens but it’s pretty uncommon and the structure of Wikipedia means that it only really stands on fairly obscure articles.

It’s also true that Wikipedia does have an inherent western liberal bias. It’s subtle but it is there and results from the fact that for the majority of Wikipedia editors western liberalism is the water they swim in. Any claim that is counter to this ideology needs to be cited up the wazoo whereas claims that are confidant with it will often slide without citation. Those with a strong attachment to an alternative ideology often find it infuriating.

Finally there are individuals who would rather have the arbiter of truth be the powerful rather than a relatively democratic institution.

All that said Wikipedia is a remarkable achievement and an invaluable part of the internet.