I can see the discussion here but i would say that altcoin help Bitcoin a lot in terms of New users being introduced to bitcoin. I also believe that altcoin are not used only for trading or so we say useful. But instead altcoin are somehow a testing grounds for some possible update to bitcoin in terms of application with regards to masses' reaction.
If we check the forum activity we can see that the most popular board is altcoins so I understand that many people were/are introduced to cryptocurrencies through these altcoins and learn more how these work and learn the power and the potential of bitcoin.
altcoin move faster than the bitcoin if on price don't be surprised if altcoin more widely discussed because potential and the amount of altcoin, especially by traders
beside that, without altcoin, we only can trade bitcon with fiat and its hard to make a big money but if we doing trade bitcoin with altcoin, then we can make a big money because we know that for some altcoin, there is always get a big jump in the price so we can getting much of profit.