It's throw away lines like this that make the BBC and others like it lose credibility to me.
If you're going to make such a claim, the least you can do is cite at least one example.
I've never seen or heard any conservative in the U.S. laud Japan's "racial purity".
What utter nonsense.
You can take a look at the process of naturalization (becoming a Japanese citizen): "Those who wish to be naturalized must either have no nationality or, in principle, lose their nationality by naturalization."
Hence you could argue that this provision forbids foreigners that integrate into Japan nationality in remembering and being connected with their past identity (that might be seen as lacking purity).
I haven't ever seen anything like this in any sort of main-stream conservative media.
I think that making claims like this discredits the reporter by exposing a clear bias in reporting.
Of course, it's possible that I just haven't seen it. In which case, it should be easy to find and cite an example - but a cursory google search doesn't turn anything up for me.