Badness in wine - who decides?

This weekend, I watched the film Eat, Pray, Love and found it self-regarding, superficial, privileged, conceited and abominably written. Generally speaking, it was badly received by film critics too. Yet it grossed $205 million on a budget of $60 million - so plenty of people enjoyed it.

Recently, there has been some argument among wine critics about 'bad wine' and whether it should be promoted, condemned or ignored - for example, this Eric Asimov piece in the New York Times, which includes links to various other threads in the argument from other writers. But rather than stoking that fire, what interests me is how badness is defined in the first place.

I could comfortably argue why Eat, Pray, Love is a bad film, but some of the people I watched it with enjoyed it. They didn't even necessarily disagree that it was bad, but were able to find enough merit to make it a worthwhile experience - Julia Roberts acts well, some of the cinematography is quite pretty. Is it valid to enjoy the film on those grounds and ignore its bad points?

For wine, as for any matter of opinion, herein lies the quandary: experts have the knowledge, position and authority to make pronouncements on quality - yet calling something 'bad' is bound to alienate lots of people, especially if that thing is unashamedly populist.

On the one hand, any critic who only writes positive reviews and never says what they dislike (and why) comes across as toothless.; on the other hand, if it's only a matter of opinion, perhaps negativity is uncalled for - especially in the wine industry, where the relationship between producers and writers can be very close. What if I say that Petrus is bad wine? Okay, perhaps the consensus of opinion is enough to prove me wrong - but what if I say that a certain natural wine is bad? Suddenly, this is much more inflammatory.

What makes me uneasy is any sort of proclamation from the wine world which makes people feel stupid or wrong for enjoying what they drink. It is this exact feeling which I think leaves so many casual wine drinkers distrustful of the wine world, in fact.