This is such an interesting and common expression of humanity. We tend to exhibit enormous individual hubris, and then express deep humility about our entire species...
Why shouldn't we believe that we are an exceptional, advanced life form? What reason is there to not believe that all other "inhabited worlds" are inhabited only by algae?
Drake's equation doesn't take into account the events -- improbable events -- that led to human life on our own planet. Many factors, from our large Moon to asteroid impacts to oxygen-producing cyanobacteria to dramatic climate change, all seem to have been crucial in our evolution. Even if the galaxy contains several hundred planets that could support advanced life, it's unlikely that any of them experienced the same kinds of events that the Earth experienced on the way to evolving intelligent life.
I also believe that the universe is so large, and other stars so distant, that it greatly inhibits any one intelligent lifeform from finding any others. Sure, the world looked enormous to travellers only a centuries ago, and now we can fly to Hong Kong in a few hours and sip wine in a leather chair -- but that was just a matter of technology.
Communicating with (and travelling to) other inhabited planets might be physically impossible. Imagine if we eventually discover another civilization broadcasting their own radio signals even so "close" as the Andromeda Galaxy. A conversation will take billions of years. Travelling there is essentially impossible. Even at ultra-relativistic velocities, the people aboard the starship will have to procreate, live, and die for thousands of generations during the journey. Who knows what "species" would finally show up at the aliens' doorstop?