Wait a minute!
How many people do you think wander into large forums with the expectation, "I need to be on my guard or else I will be scammed, because the forum allows scammers to stay here."
The internet is full of scammers and scams. Even if you receive a phone call from a random number, there is a good chance it is a scammer calling.
Scams are not limited to this forum, and people need to use their own good judgement in order to judge if something or someone is a scam.
You can make someone type a message saying they understand someone they are dealing with is a scammer, and you wouldn't be telling them anything they don't already know.
If there is a case of a specific warning not being obvious to someone giving scrutiny, this should be addressed. But blanket, generic warnings is probably unnecessary and may result in someone missing a specific warning about a potential scammer.
There is an adage that says "a fool and his money are soon parted" and this likely applies to many victims of scams on this forum.