Some of the Nintendo bashing I would say is against Nintendo fanboys, which is not Nintendo in itself, but is arguably related to some degree. As for the other occasions, I think that people think that saying a game sucks is being viewed as a valid opinion if it has no back-up.
Because Nintendo is kind of what brought us all together to some degree, disagreeing or disliking Nintendo things should require some back-up, and in the same token, things that are not Nintendo should not be bashed in the same fashion so we don't look like Nintendo fanboys.
There are some things that Nintendo has done that do not please everyone, and in general with the price of video game software down compared to what it used to be in the past, back when there were cartridges, people here are now more able to buy various games for various systems. Not to mention pirating is easier now, lol. Ultimately though, Zelda and Nintendo are single interests, and to not have more and to not see the good in other things is delusional. The tone of how things are talked about could be a little less harsh though.