Are imperatives considered rude if they are used without "please" and "kindly"?
Please, go ahead.
Give me the eggs
Please, give me the eggs
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In my experience (in the Midwestern United States) I would recommend the following:
When you are using an imperative in a way that benefits the other person, it's not common to say please, and it's not rude. 'Go ahead', 'take one', 'let me know if you need help', are examples where you would not say please because you're really offering the other person something.
If you're using an imperative to ask someone to do something for you ('Give me the eggs', 'help me move this'), then it would probably sound rude to not say please. However, people will often phrase it as a question: 'Could you give me the eggs, please?' 'Can you help me move this, please?' If it's phrased as a question, please is not necessary, but it makes it sound more polite, especially with people you don't know very well.
An exception to the second case is that people who are friends will often use the imperative without saying please and without phrasing it as a question, because it's faster.
Expectations regarding explicit markers of politeness when an imperative is given are highly context-dependent (and not just in western society, of course).
They will be affected by such things as the urgency of a given situation; the setting (e.g. school, workplace, army); the existence of a hierarchical/power relationship (or lack of it); the existence of prescribed communication protocols (e.g. air traffic controller/pilot); the degree of familiarity or emotional closeness/kinship shared with one's interlocutor; the difference in age (e.g. adult/child); and individual temperament or personality. What might be considered rude behaviour in one situation might be regarded as efficient communication in another.
I'm sure I have left out quite a few other variables, but I think you have a basic outline of what kinds of factors and constraints might be relevant.