Most people usually sell altcoins to buy bitcoins because we all know bitcoins are the best and most investable coins in the market. There are very few people who do the opposite so it's no surprise that no one agrees with your idea.

But in my opinion: it is a portion of the profit you make from your bitcoin investment and although there is a risk, it is clear that you are investing with money you can afford to lose and not with your initial capital. So I don't see any problem with this idea but at the end of the day it's your money and you are the only one responsible for it. You should consider carefully when making decisions instead of relying on other people's advice when we are not the same.