You are stuck with the people in your league all season. You never know who will end up owning the guy you want to trade for just before the deadline, and its best not to have enemies at that point. There will always be idiots in every league, not matter if its paid or free, ESPN, Yahoo or CBS. Get used to it. But try to avoid confrontation. Every owner is a potential trade partner, and both sides are more likely to end up happy with you go the extra mile to keep the peace.
The same idiots who make trouble in your leagues are the idiots who will decline all your offers just to spite you. It really is a pain to be making a very fair offer and not get any response, simply because they don’t want to talk to you. Be the bigger man, and it will pay off later on.