Some of the most basic, profound and unresolved ethical questions of our time centre on questions of when it is right to accept or even celebrate differences, and when it is right to condemn those differences. Usually people come down in the latter camp when they view the differences in question, or their outcomes, as immoral.
Wertperch in his writeup elsewhere in this node approaches this from the angle of dietary choices, which are often seen as purely personal decisions, and then he broadens the scope a little to look at religious differences and the strife they can cause. I see a similar dynamic at play in many other arenas too, and although I think it's sensible to be extremely wary of taking an adversarial view on moral questions, very few people would dispute that there are times when saying "I'm right, the rest of you are wrong" is justified - the only question is where we draw that line. See how many of the following you would agree are just wrong, and how many you think are valid ethical choices, part of the rich tapestry that makes up modern human society.
- Killing and eating humans, because they're tasty
- Killing and eating humans, because they're too ill to live already and otherwise you'll all starve to death
- Killing and eating humans with their explicit, well-documented consent
- Killing and eating pigs
- Waiting for pigs to die of natural causes, then eating them
- Waiting for humans to die of natural causes, then eating them
- Killing pigs just for a laugh, then setting them on fire
- Keeping humans as sex slaves
- Keeping pigs as sex slaves
- Keeping pigs for sex, but the pigs are totally into it
- Keeping cows for milk, killing them and eating them after long, comfortable and well-fed lives
- Keeping cows for milk, in tiny cages, pumping them full of hormones, feeding them on cheap processed feed, taking their offspring away from them at birth, then killing them in their prime
- Having gay sex
- Despising people who have gay sex
- Locking up people who have gay sex
- Despising people who want to lock up those who have gay sex
- Locking up people who are opposed to your regime, potentially violently so
- Violently opposing your country's regime, because it locks people up for their politics
- Violently opposing a regime in a country that has nothing to do with you, for political and ethical reasons
- Leaving the light on when you pop out of the house for an hour
- Running an enormous SUV that you never use for any journey you couldn't have walked on foot
- Setting fire to forests
I'm suspicious of easy answers here, and I know that people's moral intuitions often disagree on these sorts of things. It's vitally important in a multicultural society - in a multinational world, for that matter - to acknowledge that other people will reach different moral conclusions from you, and to some extent we surely need to respect those differences in morals.
The thing is that respecting someone's morals means respecting their condemnation of people who don't share them. If you think I'm wrong to condemn someone who would kill other people for fun, you're really not taking my moral stance very seriously. If I think someone is wrong to condemn people who have gay sex, that's because I do not respect their moral stance.
If someone's moral positions lead them to hurt those that I care about, then viewing them as 'the enemy' becomes quite reasonable - although perhaps not optimally helpful, from a diplomatic standpoint. From the point of view of someone who cares about the well-being of homosexuals, their persecutors are, in some sense, 'the enemy' - or at the very least, a problem. From the point of view of someone who cares about the well-being of animals, people who knowingly participate in their brutal exploitation are 'the enemy' in much the same sense.
Fighting injustice demands not acquiescing to the moral judgements of others, when we consider them wrong and harmful. I know that few people have much time for self-righteous vegans, and for my part I've long felt like I can do more for the vegan cause by not guilt-tripping people or insisting on my moral superiority... but then, nobody has much time for other people suggesting that what they're doing is morally wrong - the same goes for thieves, bullies and slavers. I tend to think that while it's always tiresome, it's only wrong to make someone feel guilty if they haven't actually done anything reprehensible.
I can well understand why someone would get sick of people getting on their high horse about things, but in my adult life, I have witnessed meat-eaters moaning about sanctimonious vegetarians at least as often as I have witnessed vegetarians actually being sanctimonious. That is to say, I regularly see people getting on a high horse about other people getting on a high horse. It's a pretty weird phenomenon, when you stop to think about it.
I want to be clear here. I'm not saying that meat-eaters are on a moral par with slave-owners, and I'm not saying that we should go to war in defence of animal rights - or gay rights, or even women's rights, for that matter. I'm not saying you're an awful person if you don't see any of those things as particularly important. I'm not even saying it's cool to make people feel like crap just because their personal choices are inflicting needless suffering on other sentient beings, or contributing disproportionately to environmental crises that we are all collectively bringing on. My point is just that a great many different sorts of people are guilty of smug superiority, and while it's perfectly understandable to get sick of people standing up for what they believe in, if you take the time to think about what they're getting worked up about, you may well find that they have a point.
Or, on the other hand, maybe they are just wrong...