Okay, so this is an old bugbear of mine. But usage seems to be a growing problem, even for supposed professionals, especially amongst those broadcasting on TV and radio, who should be ashamed of themselves!
It’s really quite straightforward, you know.
If you’re not interested, the term is uninterested, in line with most similar opposites. You’re either dressed or undressed, moved or unmoved, reasonable or unreasonable, so, similarly, you’re either interested or you’re uninterested.
If, however, you’re politically neutral, you are disinterested. If you’re making a judgement without bias, you need to be disinterested. Disinterested means without bias, impartial, neutral.
‘Jennifer was uninterested in football, so didn’t care which side won.’
‘The referee was disinterested in the outcome of the match and remained neutral throughout.’
Does that help?
We have such a subtle and comprehensive vocabulary in English; it seems a shame not to use the right word, when perfectly good examples are available, don’t you think?