> I mean it in the same way you'd put a "not to be operated by morons" sticker on dangerous industrial equipment.

I've never seen a sticker like that on dangerous industrial equipment. I'm pretty sure if you tried to put a sticker like that on dangerous industrial equipment, you would not limit your liability one iota. You would certainly receive at least this much pushback, and probably more. Normally, for a warning to be effective, it needs to say what it is warning about.

>Redis offers little to no guarantees, particularly in a cluster, and unless your data is perishable (session state, cache ...) and you now exactly what you're doing, that's less than what most users expect. I've seen it happen several times already.

It reads like you're making a different claim now than you did before. Before, you said something like "you're an idiot if you use Redis as a database", and we were concerned by what you mean by "a database" and how useless it is to just call someone an idiot. Now it seems like you mean "you'd have to be an expert or an idiot if you decide to use Redis at all for any purpose".

Now, I think it's still useless to call someone an idiot - it would be more productive to play with a cat than call someone an idiot for using a widely regarded tool.

In this form we don't need to worry about what you mean by a database - it's the tool that is the signal, and you need to take into consideration its properties before you decide to use it, rather than reading marketing copy or looking for a point on your resume.

And I think trustworthy, expert, well-trained people can make judgements that turn out to be wrong. A person can make a very good case to use Redis which turns into a nightmare by future requirements changes or by an incorrect weighting of the pros and cons.

I think you're just trying to say something which I would express as "The burden of proof lies on the person who wants to add Redis to a system, and on any additional use of Redis in a system which already has it. If you're considering simplifying a system which uses Redis and something else so that it uses only one of them, you almost certainly want to remove Redis rather than the other tool." If so, I think that's fair (even though the word "idiot" will make it harder to get your message across, and the mention of "as a database" is a distraction - you can only use Redis as a database and the question is how much persistence do you need and how much do you get), but I think you should have added the why to the original message: "Redis offers little to no guarantees, particularly in a cluster, and unless your data is perishable (session state, cache ...) and you now exactly what you're doing, that's less than what most users expect." Like this, it emphasises the risk of "accidental creep" as well as the persistence limitations you're worried about.

After all, any idiot who reads your original text is going to ignore it. If they're willing to decide based on reputation, Redis is a well known tool used by many businesses and you're a pseudonymous commenter on social media. If they're willing to decide based on facts, you didn't give them any. And if they're willing to decide based whether or not they assess themselves as an idiot, they aren't going to assess themselves as an idiot.