It's probably much easier to define a culture other than your own because you can do so in a much more stereotypical way. If you asked a Japanese or Australian person to sum up their culture to a child they would probably have quite a lot of difficulty with it as well. People tend to see members of their own group as more individual (or unique/diverse) than people of other groups, people in other groups get lumped together as 'them' and 'they' have particular noticeable features which make them different from 'us'. Being outside a culture I think it is difficult to understand the different nuances within that culture, also western culture is not the only one that adapts and changes with outside influence. The idea of culture as a static thing is also rather naive, again as with other cultures we look at our historical culture from a simplistic point of view. It's easier to focus on the dominant discourse (for want of a better word) or the time, rather than to look at the variations and influences on that historic culture over time.

Regarding all the awful things that humans do to each other, I think it's too easy because we've evolved in a way that has let us advance to technological and ,in a way, intellectual supremacy to think that 'humans' are much better than other creatures. We had certain traits (opposable thumbs :P) that lead to an opportunity for us to develop, when the right motivation presented itself, more than other animals (this is highly simplified of course and not based on any sort of scientific evidence, but I do believe that humans at the start weren't destined to be special and that other creatures with the right catalyst could have developed into the dominant species instead. Some members of the crow family and also chimpanzees have shown tool use for problem solving, but given the status of humans they would never have the chance to develop that into what we have now). Our society is something which has been developing from animalistic roots and is something that will always be developing, territorial fights are not uncommon in the animal world and whilst I've heard that animals generally don't kill others of their species, given how numerous humans are it's probably not that surprising that we can (as on a species level the deaths of members of the species will not impact it's future survival adversely **discalimer** I am in no way, shape or form condoning murder of anybody for any purpose, merely pointing out that as a species you can see why we might have this behaviour when other animals do not).

The values (or virtues if you prefer) that our society has developed (remember also that not all cultures are monogamous) can broadly be seen to either a) cater to the survival of the species as a whole and/or b) to further the interests of those in power, the origins of our cultural values are too complicated for me to understand/find out and probably would take far too long to be written here (and then contested by people with another interpretation of it and so on). Bottom line is we have certain ideals which are aspired to (attractiveness, wealth, monogamy and so on) and which we need to confirm to to some extent to fit in well in society. I don't see the idea of 'mate for life' as a lie, more as an aspiration which many people may never achieve but which we still value as a society. But it's not something set in stone, with seperations becoming more common we are getting more realistic expectations for relationships in the world we are living in at the moment. Also bear in mind that a changing rate of divorce doesn't mean that people are any less happy in their relationships, it may just reflect that divorce has become a more acceptable thing and the stakes aren't so high (back when men owned all of a womans property once they married and had sole rights for childcare I'm pretty sure there weren't many divorces, I'm also pretty sure that not all marraiges were happy).

We are social creatures, a solo human doesn't really have great odds compared to other creatures when left alone, you could argue that with the technology we have a human could survive perfectly well, but that technology was developed collectively, not by one individual. Not being 'real' with each other is one reflection of the way in which people adapt to try and fit in with the rest of society and also to gain greater power within it. It is, perhaps, a negative impact of people trying to conform to societal norms, that being said if everyone was completely honest with each other it doesn't mean that the world would be a better place.