I think that investing in altcoins is part of the process, it's difficult to find someone who, at a certain point, didn't buy some altcoins with the hope that they would outperform bitcoin. And it happens, it's not easy to find the right ones but it's possible. I don't blame those who decide to take this risk.
Of course bitcoin in the long run is the best and safest choice, just a small part of money should go toward altcoins.
You are right, however, the thought behind investing in altcoins by most people isn't that they are going to outrun Bitcoin but it is the potential for quick profits that altcoins are known to generate. When you make an investment in Bitcoin, you tend to expect a longer process since it has a high value which makes it less volatile. Expecting 10% profit from Bitcoin within a day is a lot to expect, but expecting 20% from an altcoin priced around $10 or something is easily achievable.
Those who understand the market very well would know there is no harm in buying altcoins as long as they know when is the right time to buy and when is it to sell them back to secure some profits. You can always have Bitcoin in your portfolio, but as I said, you will probably expect profits being generated from that in a longer period.