The most serious concern for me is the lack of respect and care shown for others as real human beings in some people answer their posts, especially when they don't believe their spiritual views.
We should always remember that there are REAL people behind the posts, and the manner in which we respond to them and the words and tones we use can really hurt and bring them down far beyond the press of the "post message" button.
Let me draw a parallel with this to some other scenarios: like that of firing a missile from a long distance away by pressing a button, or dropping a bomb from a plane high up, or firing a weapon from behind a cover. In all these cases where you can't see the people on the receiving end, the effects of the weapon are not lessened, and nor is the responsibility of the person firing the weapon. They still wound, maim, hurt and destroy, or cause traumatic stress, long after the button pusher has moved on to something else, perhaps even laughing at the perceived stupidity of the receipent(s).
As others, such as sunshinemmum and lottieandmias, have said, ask yourself before you post something negative about an individual's belief or viewpoint, whether you would use such a tone and language to a good friend you cared for who was standing in front of you, even they happened to express a viewpoint with which you didn't agree? If not, then don't post that message! Instead, rewrite it in a very different way - one which simply expresses that you don't agree with it and why from a personal point of view, and completely refraining from adding statements of personal derision and attack.
I do not personally believe such white feathers are angels, nor are left by them as a sign. But I would be happy to have a friendly dialogue/discussion with someone who did, explaining my viewpoints and hearing theirs. But I would never dream of attacking or putting them down personally. As others have pointed out, there are good, non-personally attacking ways of doing this, and those are the only ones that should be used in any such discussion, whether online anonymously or in person.
Remeber that you never know what state, background or situation the anonymous person you are posting about is in. Something personally negative that you say, maybe even without much thought, could really hurt and push them into depression, etc. They've probably come onto this forum in an unsure state seeing support in the first place.
SO REMEMBER BEFORE YOU PRESS - there's a REAL HUMAN at the other end of that button!
Always have love, care and respect for one another, whether you know them or not, and in so doing, some form of heaven (whatever your beliefs or not!), will then exist on earth and be shown through you.