Yes we need altcoins but we do not need more then we already have i think we have like 1200 coins in total and nobody follows them all everyone follows the most popular ones and they only try to follow one if they see how much they can make.
I think yes we need altcoin because with altcoin we can have a dream to succeed, if we do not have altcoin we can not have much profit and if it does not have altcoin what would be bitcoin if without altcoin since altcoin also depends on bitcoin,