Any investor that does not have a discretionary income does not need to invest in bitcoin because if he does, it means that he is gambling and he will definitely run at loss because that is always the outcome of gambling.
I agree with you. But I cannot agree with the comment that one should not invest if there is no discretionary income. Nowadays there are very few people who cannot save $25-$35 after meeting their monthly needs. Out of necessity people work hard but earn extra money. Nowadays people thinking about their future keep their fiat in a savings account in banks or various NGOs. I think investing in bitcoins might be a better choice than putting money in this savings account. Because Bitcoin savings offer higher returns than bank savings, Bitcoin savings tend to last longer than bank savings. I wouldn't say to invest the entire savings in Bitcoin. You can easily start investing in Bitcoin by investing $25-$35 i.e. $10 out of $30 in Bitcoin, $10 in bank savings and $10 in an emergency fund. $10 is a small amount but very beneficial for low income people. If you have less than $10 to invest, you can start investing by saving $20 every 2 months. If one can successfully extend his investment for at least 4 years then after 4 years he can save 12×4×10=$480, calculating the profit from this due to increase in value of Bitcoin he will easily get back $700-$800. Where he can connect some money and find a small source of income.