I'm saying the Voyager probes don't make a counter example to interstellar travel being impossible. That's still very much an open question. We might be able to develop adequate shielding to protect spacecraft from radiation over mildly geologic timespans, but we might not. I'm certain it won't be as easy as you seem to think it is.

(Unless you count slinging a dead pile of former computers through a distant star system as successful interstellar travel, but that's not what most people are interested in.)