I don't think if it's good to buy altcoins if you just short trade only we don't know if it will decrease more, but for long term I guess this is the right time to buy and hold until the price will recover.
The market in particular is currently experiencing a significant decline when yesterday happened and yesterday it was reported to be making the price of bitcoin a big decline. so when we want to buy bitcoin now this is the right moment. if we are indeed an investor, of course now is the right moment to invest or take advantage of this condition 
Source :https://cointelegraph.com/news/friday-shows-bloodbath-for-crypto-markets-bitcoin-price-at-7-300