And therefore I don't really understand the unfortunately sometimes very emotional discussion between "major" and "minor" lithuanians here in this forum.
There are no "minor" Lithuanians in this forum. You probably mean a German (Lutz Szemkus) of ("minor") Lithuanian origin. If he had to discuss these matters with the real "minor" Lithuanians (although few thousands of them survived), the discussion would be not less emotional.
But I guess to accept that people not nessesarily have to belong to absolutely only one "nation" or nationality is very hard for "national" thinking people.
Well, a person may have ancestors of various nationalities, but I really don't think, that it is possible to describe a person as being 5,3% German, 6,8% Lithuanian, 9,5% French, 5,9% Russian, 2,1% Polish, 4,6% Hungarian, etc., etc. All these percents are equated to zero or 100%, when the person with this ancestry chooses his nationality. (And this do not necessarily mean that he now must disregard or scorn his ancestry of other nationalities.)