I think you cannot compare cigarette warnings to those proposed here. The warnings posted on cigarette packs are general knowledge - every smoker knows this since these facts are known for a long time. In addition, smoking warnings apply to every cigarette. So smokers don't care about them...
In the case of cache warnings, these new proposed warnings are not general warnings for all caches out there. The warnings are cache-specific. Thus, before reading them, you cannot know what the warning content will be for that specific cache you are looking for in the moment.
Next thing is, the usual logs are not sufficient enough to post important warnings. No one reads all logs, if someone says this, he is lying. Imagine there are 100 logs and one important warning is 50 logs away: most wouldn't notice even if they read logs. With a special log type this can be different: you scroll down the cache description, you come to the beginning of the logs section, you see: 123 finds, 5 dnf, 10 notes, 3 warnings...
3 warnings? Hmm wait, shouldn't I click to see what is in those warnings??? I think I would like to know...
If you don't like such a feature, just don't click to see the warnings, just ignore, it's up to everyone. Some might read them...
And one key statement is:
It's just wrong to say no one reads cache descriptions, no one reads logs. Most people I know do so. But as stated before, this doesn't mean to see all logs and to get every important information out of them. But if you see there are warnings...
And one last point: some said they don't think people would use this feature. This is wrong. There are lot's of cachers out there who do post warnings in their logs, who care about others...