Great post! It's just way too easy to be offended or offend (unknowingly) others on the internet. Written word doesn't hold tone of voice, emphasis, etc. so things can get taken completely wrongly.
My rule of thumb is just to let things be. I try my hardest to be courteous, but know for a fact that I've offended on the net before. At the end of the day, it's just the internet. If someone on here says something that pisses me off, big deal!! I can close my computer down and life goes on.
As for things specific to this board, I've learned my lesson early on! As a vegetarian, the posts about processing birds are simply not appealing to me. So, I stay away from them. I have happened into a few of the aforementioned threads unknowingly because the title wasn't very clear, but I take that on as a risk of being part of a board for chickens.
One of the best things about the internet, I feel at least, is the lack of censorship and the fact that people tend to open up more when hidden behind an anonymous screen name. No if ands or buts, if you're on the internet, you're going to come across questionable/offensive/inappropriate content.
I just think it's silly for us to get angry with each other over these small things. It's life--not everything is candy and roses or only things you like to see. Let's remember to take personal responsibility for the things we view. It's not at all difficult to stay away from the things you are uninterested in. It's just way too easy to blame someone else when you've seen something you dislike.