I have been a forum user for many, many years, though I am new (ish) to MN.
A few things I have learned over the years:
I use forums where the majority of the people seem to have similar views and values to mine.
If it is a personal or sensitive issue, where an opposing opinion could cause me upset, and I could not trust myself to let it be, I generally wouldn't post about it. Of course, there are times where I have reacted shamefully, but I doubt you will find any forum user who hasn't at least once behaved in a way they wish they hadn't.
You have to take it for what it is. A strangers opinion. If you care that much about strangers opinions, you need to work on your self esteem and confidence. The problem is most likely yours.
Perspective is incredibly important, and remember, there is no tone of voice in the written word.
I have posted a couple of times in various areas on here. I have also had replies that have made me recoil. But I saw them for what they are. Someone else's opinion. And if anyone made anything personal about me, I would definitely fight back, as I don't think anyone on here actually knows me. But I have yet to come across such attacks, on myself or someone else. I like MN because everyone seems to make it clear that it is opinions not fact that they are giving.
I hope you learn from this incident, and remind yourself that we are all strangers (unless some of us aren't!).