Interesting...This possibility fills me with profound dread. People meeting other unknown alien people has happened in this planet in the near history _so_ many times. And not in a single one of those meetings was there anything to feel mushy about. It was blood all the way. Pizarro and Atahualpa didn't sit together and play chess over a hot cup of coffee and exchange notes on their childhood crushes.
Let's say you run across an alien during a walk in the woods. How could you ever tell whether the alien was friendly or not? Aliens might act friendly, right up until the time they put you in the big alien stew pot. Likewise, friendly aliens might use deadly force and extreme caution to make sure you pose no threat. Would you want to be sending "Howdy There! We're new in the block! Drop by for some free pizza!" messages to a civilization 20 light years away?
Long answer to bonus question has already been written and published. "Speaker for the dead" by Orson Scott Card. I am restraining myself from giving a summary here. I don't want to spoil your couple of weekends spent well. Be sure to read the introduction as well.
I must have stopped reading it fairly early, because looking at the cover I don't remember any of it. I remember the first book, however -- that super guy they brought back for Ender's training and the planet and all. It's been a few years, though. Good thing I kept all the books.
I think Orson Scott Card wrote "Speaker for the Dead" first and decided he needed another book just to set up the backstory. That book became Ender's Game, and he found it a bit ironic that he's remembered more for the prequel than the book he really felt compelled to write.
That depends on how much we know about them and how much they know about us. They might not even know how to act friendly and we might not know whether our potential shock and awe attack would be either shocking or awe inspiring. Knowing nothing, I for one would simply walk away and buy a pregnancy test ;-)
There's a fairly easy example of how this can go bad here on earth. Cats and dogs don't innately hate each other, but everyone knows how they get on.
The problem is that cats and dogs have opposing body language; when a dog acts excited and happy, the cat interprets that language as aggression. For example, a cat with its ears down and tail wagging is a cat that's about to fight. A dog doing the same thing is being submissive.
Of course, this all assumes that any intelligent extra-terrestrial life even has any sort of body language or capability to communicate that we can even recognize.
I've thought of this a lot. What if the alien way to show the finger is to blink or something completely normal like that? They would get pissed up fairly quick.
Our civilization reaches a critical point as we reach Type 1 (http://en.wikipedia.org/wiki/Kardashev_scale) and see if there is life that has already claimed the close parts of the galaxy. If there is nothing out there, we get to expand and grow. If space is already claimed, then we will probably get gamma ray bursted or something. Either way, it's something we have to and will try.
I think the greatest danger by far would be viruses. Culturally I'm not as pessimistic. Our perception of historical events is influenced by what historians find interesting. All the boring, more or less peaceful, mingling, cohabitation and assimilation going on for thousands of years is rarely mentioned.
