Yes in the general opinion, gambling shouldn't be taken or seen as an investment
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Not in general but in any opinion gambling should never be considered as an investment because the ones who gamble often get so involved in it that they forget about the risk of losses. Many gamblers lose thousands of dollars per day while investors can't risk to lose that much.
Either ways you both presented it, gambling is not an investment, the only way we can consider it an investment is on those who have invested to start a gambling business as their own establishment which I believe could have involved alot of money as well, but for any gambler who thinks he could also finds a means of living through gambling may be totally wrong about it.