By doing this you are assuming that the rise in the bitcoin price will be able to generate enough profits for your loss in altcoins. Most altcoins are connected to bitcoins in one way or the other, so a decrease in the bitcoin price will definitely have an effect on the altcoin prices, and since altcoins are priced lower than bitcoins, the rise of bitcoin will generate more profits for investments in altcoins than bitcoins in most cases.
For now, a good way to even have more of the bitcoins is to buy into some alts right now. Once bitcoin starts consolidating, some of them may start having some good momentum and with that you can be making some huge profit in your BTC holding pending when BTC bull run will start.
There has been a huge correction for the whole market and for some coins with potential, now is the time to go in on some of them.