There is no intention to take sides with Bitcoin fans or Altcoin fans, but if you realize this is like a marketing strategy in selling. Between Bitcoin and Altcoin there are options, when there are BTC and ALT new people tend to choose between these two options, even though it's all still in the cryptocurrency pool. Meanwhile, if there is no ALT, investors most likely have other choices such as FIAT, gold, shares or others. It is clearly out of the cryptocurrency space which actually makes the existence of cryptocurrencies unpopular.
Altcoins are quite attractive for new people, and Bitcoin is attractive for long-term investments. I think the two really complement each other.