I agree that society has become polarised, and think it happened deliberately. Nobody benefits as we are all part of on group or another that someone else has learnt to despise, and it's unnecessary, as generally people have more in common than not, so it makes sense to concentrate on that, rather than on the points of disagreement.
I agree with AmberGran about 'facts'. Often people who believe they have the 'facts' become even more entrenched in their views, but IMO facts are very fluid when current and in any case have 'half-lives' that vary in length.
I also agree with rafichagran's post above, and with those who would prefer to see nasty posts stay up, so that the poster can be seen in her true colours. Or not, as the case may be. OTOH, I think Galaxy is right to say that there are legal implications if someone posts something libellous, so what we would prefer and what we can have are not always compatible. I find that discussion boards often work better when members speak up if they object to something, but it can take courage to do so, as there are those who will never forgive being gainsaid.
There are people I miss too - even those with whom I usually disagreed. I'd much rather disagree openly than have snide comments draped across several threads. I can happily disagree totally with someone on one topic but agree on another, and never understand why people often find that strange.
Having said all of that, we must all be reasonably happy with the way things are, or we wouldn't be here, would we? 