I see this happen sometimes, and I'm going to say something about it.
If a party leader puts up an LFM, they'll likely list difficulty. If not, when you hover over the Quest name, the difficulty will be there.
If an LFM is up for a difficulty you don't want to run it on? Make your own.
You join, ask difficulty, and it's not what you want to run it on? Leave, and make your own.
But my LFMs are not a debate class. And I highly doubt anyone else puts up an LFM with a difficulty above, or below, what they actually want to run it on.