Are humans immune from extinction?

Steve Zara made interesting post about a discussion PZ Meyers is having on Twitter.  Steve argues that humans have developed technology which is close to bringing human evolution to a halt, that we will soon leave Earth and colonise the solar system and thereby become immune from global catastrophies.

I would like to explore a counter argument: I maintain that humans are still subject to natural selection.

The greatest selection pressure of all is death of an embryo or foetus from developmental defects - such as a missing circulatory system - which make development impossible.  The majority of fertilised ova do not survive to birth, and many of these don't even make it to implantation.

We have made great strides in combating disease, yet we remain in a microbiological arms race.  Modern medicine provides an enormous selection pressure on human pathogens which are evolving to get around it.  MRSA and C-Diff are examples.

Our abilities to survive modern diets also provides selection pressure.  We have evolved the ability to digest lactose into adulthood within the last 10,000 years, since we domesticated dairy animals.  No other mammal species can do this.

We haven't colonised space yet, and in my opinion it will be some considerable time before off-world colonies become completely independent of humans on Earth, if ever.

We need only a pandemic which wipes out enough people that space travel is abandoned as an expensive luxury.  Then we are all eggs back in the same basket, and vulnerable to global catastrophe.

Finally, the very technologies which allow us to manipulate ourselves and our environments, makes us vulnerable to the failure of those technologies.  A catastrophe which disables modern communication, high-tech industry and global commerce, would leave people with complex prostheses or reliance on drugs for survival, facing imminent doom.

I know how long it takes me to be debilitated when my internet connection goes down, but if it never came back up, or I could never buy car fuel, pay with a credit card or shop for food, I'd be back in the pre-industrial age in days.

I have great confidence in human adaptability, ingenuity and ability to survive extreme conditions.  But I don't think we're any more immune from extinction than the dinosaurs were.