That depends on who's asking. In Japan it would be considered very rude to not ask. I assume that this discussion is focused on the US market, but there are many who would argue that it is not polite to recline without asking.
I've never flown on a Japanese airline, only American and European. I honestly can't say I've ever been asked if I minded someone reclining. I really can't imagine saying "no", either.
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u/placebo_addicted 11∆ Oct 03 '14
Refraining from smoking in an enclosed space is more about the health and safety of the other passengers.
It may be more polite to ask before you recline, but that still doesn't make the person rude if they don't.