Of course it's never good to allow bad arguments into the "marketplace of ideas", because then they'll take over the market, but unfortunately that ship has sailed, or likely never arrived.
Q: Who gets to define "relatively harmless"?
"Advocating for peace" sounds pretty harmless, yet if you dare to mention any specifics - at least this year - it seems supporting it is deemed anything but harmless. Before my time, but seems the same applied in 1964 – 1973.
I don't think there's anything wrong with advocating for peace, from a free speech aspect, especially if someone is sincere. (Even if someone is completely brainwashed by whatever propaganda. And even if peace itself is a super meaningless term. After all wouldn't a totalitarian world government bring peace? Etc, etc.)
Each of us defines this for ourselves, using our own moral compass.
In the spirit of fairness, should one actually no-platform everyone using emotional rhetoric?
Your favourite media outlet will almost certainly have a lot less to say if we do. Depending on your PoV, this may or may not be a bad thing.