"It seems to imply that there are no real people behind it."

In your opinion. In my opinion, the phrase "it is just the internet" means that it is silly to waste life's precious time and energy thinking/believing that you can hold individuals accountable in chat forums like this or Usenet. It is akin to saying "life is too short" or "don't sweat the small stuff". Those are good pieces of advice if you are going to post in open chat forums or Usenet.

"If you get a letter from someone which insults you or belittles your religion, mother or school, is that "just a letter"?"

Yes, although I assume (you didn't specify) you are referring to a letter that is either anonymous, or pseudonymous. Why would it make you feel safer or more at ease, knowing the name of the person who insults you?

"Yeah, it is possible to 'not open' a thread, but sometimes you have read the upsetting stuff before you realize what it is about...is it any less real because you can't SEE the author?"

It is no one's responsibility but your own to edit what you don't want to read online. Don't like it? Don't read it. Period.

No "And sometimes..." or "what if..." or "but what if someone says...". That is just childish.

"Why do folks use anonymity or psuedonyms to troll, ridicule, bait, insult, complain, disparage etc., in ways that they would probably not do if they met someone at a party?"

Same reason people who use their real names do it.

"The issue, and the only real issue is that often, anonymity is used to insult and threaten and hurt.. and to post long, tedious rants (like 'ol "Dreaded Guest" from Texas")."

Members do this quite often as well, and a person's proclivity towards such behavior has nothing whatsoever with real names, pseudonyms, or anonymity. That is YOUR bias and misperception

"I DO have a problem with THAT!"

But it is YOUR problem, not everyone's. Nor should you try to make YOUR problem, MY problem.