We cannot stop people from googling for information. What we can do is provide them with answers we think will minimize risk.
Provided that the advice is specifically related to outdoors, then it should be on topic. I think this question specifically is on topic, as it asks about a risk situation that is definitely on topic, and a potential solution (Dex).
If we want to discourage a behavior, the best method is to give good answers, upvote good answers, and downvote bad ones. Silence (ie - deleting as off topic) is not discouragement. Our goal should always be to inform. People can come read for themselves, and make their own judgement. I think that most people will not take the answer that has 10+ downvotes. This is the strength of the StackExchange system. The community has the power to identify bad advice and communicate that.
To give an analogy. Sex is dangerous (disease risk, pregnancy). Banning sex education doesn't solve that. Banning discussion of sex doesn't solve that. What helps is providing a good resource.