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.
Trading is risky and not a get rich quick scheme so if an experienced trader is approached by a newbie that wants to learn how to trade I think that it will be good for the experienced trader to mentor the newbie if he sees a genuine interest in the newbie. Mentoring doesn't mean that he will continue to babysit the newbie but he can be a guide to help the newbie to avoid trading mistakes that can lead to loses. Experience is the best teacher to attain success but it is not necessary that newbies must learn from their own mistakes inorder to be profitable traders. I'm sure that many of us have learnt a lot on this board about how to be profitable in trading without learning the hard way from personal experience. Learn technical analysis, fundamental analysis, don't trade with emotions, learn to wait and use small amounts as a newbie.