There's nothing wrong with buying an aluminum bike, and it is not slow.
It is possible to compensate its flaws by using a slightly larger tire and a stem with a slightly shorter forwards extension.
At about $600 USD, you can go just as fast and have just as much fun. For some odd reason, an aluminum bike can seriously run away from a carbon fiber bike on the downhill. That's a fun aspect.
This class of bike is well-represented in the very fast Specialized Allez Triple.
The reasons to purchase a bike in this class is twofold.
1) One may ride it for two years and then strip it, sending the components to E-bay, where they will pay for 60% of the replacement bike.
2) If one has a debt, the aluminum bike's hot performance means that you won't be missing out on any of the fun, and one can buy an all-new bike in two years that will come with all-new components. Of course, this is a form of consumerism, but it happens to be popular because it works.
I bought an aluminum bike for none of these reasons. I just happened to give it a test drive. I thought it looked very silly, so I tested out quite a few bikes. I gave the aluminum bike another test drive. It far and away outperformed all of the others, while being much more comfortable. My first and second 10 hour rides were still met with hot performance and great comfort at the end of the ride. Yes, it does run larger tires and a short forwards extension on the stem. Yes, I know the frame won't last, but I'll miss it forever when it wears out.
Ever gone dancing after a marathon ride?
Aluminum: Disposable, yet wonderful.