I don't find holding of altcoins to be dangerous, because among the entire altcoins listed on coinmarketcap very few grew while bitcoin was declining in value. But now as the price of bitcoin has started to increase, most of the altcoins too started to increase. This confirms profit on holding of altcoins.
Indeed some altcoins are now getting better in the market placed. There is no dangerous of holding it even if you hodl it for long term investment. Even the marketcap are in red situation that bitcoin now itself are in downward trends. But in everyday changes which bitcoins tends to grow it will influencing altcoins also to grow even better than before.