My question is concerning the unrelated business income tax on partnership interests inside a Roth IRA. Specifically, I own common stock in a company that's technically classified as a Limited Partnership (Icahn Enterprises L.P. to be exact), which I guess means that I'm technically considered a junior partner and get a K-1 form from them.
My question is: why is this considered an "unrelated business" for tax purposes? Unrelated to whom or what, exactly? One example of an "unrelated business" that the Wikipedia article I link to gives is a university that owns a pizza parlor. I understand how that example is unrelated to to the university's educational mission (and therefore taxable income), but I don't understand exactly how that reasoning applies to me as an individual.
And why does the tax code mandate that income derived from it be potentially taxable, even if held within an IRA? Why does the government consider this different than, for example, an "ordinary" dividend?