This belief is very popular, probably because white people want to identify with Indo-European conquerors. But it totally, absolutely, doesn't make sense anymore than the Chinese insisting that the neolithic Liangzhu civilization (O1, related to Austronesian/Daic) on the Yangtze delta is Sinitic (O3 from Sino-Tibetan). It is impossible for R1a and R1b to both be the source of Indo-European since they are geographically far apart. Looking at the y-haplogroup map of Europe its obvious that Indo-European must have originated with R1a, and that R1b folks underwent a language switch along the way. The R1b must have arrived in Western Europe before the Indo-Europeans, and they founded the famous Bell Beaker Culture, before the Indo-European Celts (themselves a hybrid of R1a and R1b from central Europe), and the Romans subsequently assimilated them. The Germanic people are even more complex, being originally I1 before being first absorbed by the R1b Bell Beaker people, then the R1a Indo-Europeans. The Basques, Etruscans and others speak remnants of the old R1b languages. This should be the honest conclusion untainted by the desire to be the conquering race. White doesn't necessarily mean Indo-European, and Indo-European doesn't necessarily mean white.