Thankyou for replying to me Starblaze.
*Well Madgran I suppose I'm just not used to anyone but my mum following me around and butting in to my conversations with other people to tell me she doesn't agree with me.
It's been used to abuse me and invalidate me, with no care for me as a person.
When it is people who you avoid and who definitely don't like you (like my mum) constantly (and I mean constantly) disagreeing directly with you, it is always going to feel personal*
I can truly understand that Starblaze.
I think the difficulty on a public forum is that when a point is made, others will inevitably read it and as part of a debate will say if they don't agree or maybe add a different perspective for consideration ...not focusing on the poster but on the point being made. If a point is being made as part of advice to another poster asking for help, then inevitably someone will tend to say that they don't agree when giving their advice as it will contradict whatever has been said before. That helps someone asking for advice to pick up on different perspectives to consider I think.
On a public forum it seems to me that there will always be some who one thinks similarly to, and some who one does not, just as in "real life". However on a public forum, with discussion written down, I think that that element of relationships is heightened and can become "bigger" than intended. It also means that the same posters may agree/disagree on different discussions as a regular occurrence.
Try to imagine how you would feel if every time you looked at gransnet, there was your name or your words in bold with "I disagree with this" without any acknowledgement or understanding of the rest of what you said or why you might think/feel that way
I can honestly say that I really wouldn't care much, its just a viewpoint on a specific point/manty different points made, not personal, just a viewpoint. I will always, I think, see disagreement as part of a debate to be a good thing, providing me with different perspectives to consider. However I can see why, with your experiences, you might see it differently
*Unfortunately I can't just change how it makes me feel because someone else says I shouldn't be bothered by it. I can only work on it for myself.
So there we are, perhaps it will stop now, perhaps that behaviour will be enabled further.... let's see.
If not, I've said what I think/feel and to be honest, its really not bothering me nearly as much recently and I'm getting really good at just ignoring people who want to hurt me. My mental health is more important than people who really don't care or understand me*
I'm not sure why you see disagreement in a public forum discussion as wanting to hurt you but again I can imagine that your experiences that you have described might well trigger that response. It is good to hear that "it" is bothering you less than it used to, that is personal growth isn't it. 
"Enabling" of behaviours seems to be to be another perspective on people discussing, agreeing with some things, not agreeing with others. Again I suppose one's different experiences can influence one's interpretation on that especially if comments are seen as personal as opposed to part of discussion.
I am wondering if you also notice when your name is highlighted because someone is saying that they agree with you?
I've quite honestly seen these adult children along with cruel and abusive and never a reason for estrangement and let it go because upset people say upset things. I have even patiently answered people questioning me for estranging and thinking I shouldn't have
Yes upset people do say upset things. In my view you are entitled to give a viewpoint on that, which might well be helpful for others to consider another perspective - maybe part of their personal growth? My understanding is that you feel that it is kind to not comment; others might feel that it would be kinder/more helpful to give an alternative perspective. Different viewpoint, both valid, just different.
I am conscious that in saying all the above it can be seen as disagreement and perhaps be interpreted as "trying to hurt", within the context of this discussion. That is not the intention at all. I am trying to explain my own perspective on discussion and debate, presenting a different viewpoint. Your perspective gives me food for thought. Thankyou for that.