Nowadays, the market share of Bitcoin is going up and the altcoins are dropping even faster than BTC. Some of the important altcoins such as Cardano and NEO have lost as much as 95% of their value from the peak price. So it makes sense to sell the alts.
If you are going to sell those alts, it means that you already lose and it only tells that you are not patient enough to wait for the bounce. The sun is hiding behind those clouds, the same thing with crypto. After this dip and for sure there is a bottom of this, we can recover though not all but at least the losses that we incur is minimal.