It means what they're saying shouldn't be complicated, plain and simple.
In that case it is self evident. I see people using it here as a way of adding authority to their opinions.
It has nothing to do with authority. It's more likely that the poster thinks that someone is over thinking what seems to them to be a simple issue. You are in fact doing that now, by adding the idea of an argument from authority to a term that has nothing to do with it. You need to look at the plain and simple meaning of "plain and simple".
If you do xxx than you are xxx plain and simple.
Why do people on this forum say this? It doesn't make the point inarguable by adding this as it adds zero authority. Just curious. I think this is a case of phrases rubbing off on others.
Yes but only if the issue is actually simple.
I've seen it used like this:
That is an opinion piece and it's neither plain or simple.
Well their opinion is at least very simple. They've distilled the requirement for being labeled something down to a single variable. Now whether what they say is factually true or not is another matter.
If you're lacking in both intelligence and looks, you're plain and simple.
OP, remember, your name used to be iamanidiot, so....yeah.
In that case it is self evident. I see people using it here as a way of adding authority to their opinions.