Instead of trying to stop these newbies not to go on trading because of their lack of experience and skills, my advice is, let them trade and experience on their own how risky trading is, that way, they will learn trading the hard way. And for sure, the next time they trade, they will prepare for it to avoid further losses.
If you allow newbies to go into trading without acquiring knowledge they will end up learning the hard way no doubt but they will still find it difficult to learn since they will be trying on their own with no mentor to guide them. Experienced traders also encounter losses though not like the newbies i think instead of allowing them to waste money that will be useful in doing other useful things in the name of trading without experience it is because they are encouraged to get a mentor that will groom them before they can start doing it on their own.