It is similar to religious movements. You find Christians shouting at each other over the difference in a bible verse, although their belief structure is 99% the same.
National Socialists and International Socialists are similar. Their programs are very similar, but relatively small differences are pointed to to claim they are completely different!
The major difference between the two are set forth in their respective names: National and International. Their methodology is pretty much the same; they only differ on how the end plays out.