Those 2 words. Says it all.

Because you're only looking at two words. The full sentence was:

We can't shield against cosmic rays with any currently-existing technology, nor are there any real prospects for developing a material that can do so over the next few decades.

If you misread what other people are saying, then you won't be able to have a productive discussion with anyone.

You know the difference between those who want to see us head out to the stars and those who will be doomed to stay put? People who can accurately assess what the current level of technology is, figure out what changes have to occur to current levels of technology in order to make deep space travel, and thus actually develop a plausible roadmap for getting there. The people who blind themselves to the existing state of technology will never be able to accomplish anything, because they won't be able to accurately identify what has to happen for the goal to be fulfilled.

We do not currently know how to shield astronauts from cosmic radiation. We will need to figure that out before we can have a Mars colony. Pretending that's not true because you think it's inconsistent with a "can-do" spirit would be foolhardy.