"Never" is a very long time.
I don't think it is likely that humans will go beyond Mars in my lifetime (say the next 50 years or so), but never? Claiming that is just hubris. There is no way to state this with any degree of surety.
It is not a stretch beyond credibility to assume that humanity may be around for a few thousand years yet. Given all we've done in just the last 200 years, almost anything is possible given another 2000 years.