Part 1

The "double genocide" model is generally evaluated and criticized heavily since most texts that propose it are not works of serious scholarship but rather political efforts that try to affirm a national narrative of victimhood that is used to advance a nationalist, often prejudiced and anti-semitic agenda as well as to avoid discussion and/or research on the totality of the impact of Nazi and Soviet occupation on various Eastern European societies, in that collaboration with the Nazis (and even with the Soviets) is regularly ignored in favor of concentrating on victimhood alone. This "model" is not so much a serious academic effort to explain history but a politically (often imposed from above) narrative in order to legitimize certain political agendas.

Two things that need be mentioned first here:

The term was also used to great effect in a controversial book of French journalist Pierre Péan Noires fureurs, blancs menteurs (Black Furies, White Liars, 2005) about the genocide in Rwanda. In it, Péan asserts that the Tutsi's "culture of lies and deceit" as well as their oppression of the Hutu and the violence of Tutsi militias during and after the genocide in 1994 constitutes a double genocide during which the Tutsi also massacred the Hutu. While this did garner some support, among others from government minister Hubert Vedrin, here too, this thesis has been thoroughly disprove. Philip Verwimp of the University of Leuven has researched the spatial and temporal distribution of violence in Rwanda and shows that while 92% of Tutsi households lost at least one but maybe even all members during the genocide, 91% of Hutu households reported no member lost at all, thus drawing the conclusion that the structure and distribution of the violence exacted by the Tutsi lead RPF must be viewed in a different light as the violence exacted by Interhamwe and FAR.

Secondly, a criticism of the "double genocide model" as it pertains to Eastern European countries and specifically Lithuania as the most prominent example, is – and I emphasize this despite hoping it isn't necessary – not an attempt to realitivize or downplay Soviet war crimes and oppression in Eastern Europe. Rather, it is a critique of a political agenda and its underlying ideology that seeks to use the victims of Soviet oppression and crimes as a soapbox. Rather than being interested in exploration of the suffering of the victims of Soviet oppression and the phenomenon at large, purveyors of the "double genocide model" are only interested in these things as far as they are useful for their agenda. This is neither proper historical engagement of a theme nor proper memorialization of these victims who deserve to be remembered outside of a political argument seeking to legitimize heavily nationalist narratives and suppress discussion of the social impact of occupation by Soviets and Nazis, especially the issue of collaboration.

Dovilé Budryté, professor of political science at Georgia Gwinnett College, has written extensively about the the "double genocide model" both in her article "We call it genocide": Soviet Deportations and Repression in the Memory of Lithuanians and in her 2017 book Taming Nationalism? Political Community Building in the Post-Soviet Baltic States. She describes the model as follows:

According to this popular belief [...] there were two genocides in Lithuania in 1940-1953. The first one, 1940-1941 and 1944-1953, was committed by the Soviets. It included mass deportations and repressions. The second genocide was committed during World War II by the Nazis. Those who embraced this perspective [she cites e.g. Jonas Mikelinskas, a popular author or the state-sponsored Research Center of Genocide and Resistance] argued that Lithuanian Jews had actively participated in the deportations of Lithuanians and that Lithuanians had collaborated with the Nazis and participated in the Holocaust as an act of revenge.

Professional historians refute this theory and have actively tried to show it for the nonsense that it is, not just from the West but also e.g. Vytautas Berenis in Lithuania but the theory remained popular because it was and still is indeed state-sponsored through institutions such as the above mentioned center.

Budryté, Berenis and many others point out the flaws of these ideas: First of all, to portray Lithuanian collaboration as revenge for Jewish participation in the deportations is nonsense. The deportations were very much initiated from the central Soviet authorities and carried out by the apparatus that the Soviets brought to Lithuania, not by locals. Also, the deportations affected the Jewish community in Lithuania. So much so, in fact that as Atina Grossmann points out 80% of those Eastern Europe Jews who did survive the Holocaust did so because they were involuntarily or voluntarily deported/resettled by the Stalinist Soviet Union.

Secondly, the idea of Jews as the "allies" of the Soviet Bolsheviks was (and still is) an anti-Semitic conspiracy trope, which became popular after the revolution in 1917 and was an essential feature of the Nazis' and other fascists' world view throughout the inter-war period and throughout WWII that has no basis in reality. In modern terms, it very much does the same as it did basically then: Denationalizing the Jews who were killed by the Nazis because it is always easier to regard the Lithuanians of Jewish faith as Jews rather Lithuanians, especially when you want to avoid a real discussion about collaborations. Lithuanians assisting the Nazis in killing Lithuanians sounds less fitting to a narrative of national victimhood than Lithuanians killing Jews "as revenge".

Thirdly, usually the numbers given for the deportations are a bit muddled. It is generally accepted that 136.000 Lithuanians were deported in the period from 1940-1953. This number alone, when viewed in the context of Lithuania having about 2.5 million inhabitants at the time is staggering but at the same needs to be treated with caution. Because it includes a.) the Jews deported by the Nazis, b.) the German Lithuanians fleeing Soviet occupation by signing up as Volksdeutsche and c.) the Lithuanians who again fled Soviet troops in 1944. If we look at the Soviet deportations itself, the following picture emerges:

The most extensive deportations by the Soviets occurred right after the first occupation of Lithuania in 1940. Within an incredible small amount of time, Soviet authorities deported 20.000 Lithuanians to Siberia and Tajikistan. The targets of thee actions were the military and political elite and their families, who were comprised of ethnic Lithuanians, ethnic Germans, ethnic Russians, ethnic Poles and sometimes also Jews. This, among other factors, resulted in the so-called June uprising against the Soviets and the Soviets using further deportations as a counter-insurgency tactic. This process (and the uprising) repeated itself after the war in the period of 1944-1953 albeit not at the same scale and again, primarily targeted against those who had collaborated with the Germans and those who still fought against the Soviets (which in many cases were the same people).

To be not afforded due process, to be persecuted and oppressed for one's political views and to institute a policy of uprooting thousands of people from their homes and deport them constitutes grave crimes on parts of the Soviet authorities. But they do not constitute genocide, especially not on the same levels of Nazism. The genocide of the Jewish community in Lithuania was one of the most total in all of Europe, resulting in Lithuania being declared the first "jew free territory" in Europe with a staggering 200.000 victims by mid 1942. Historians of the era generally hold that to execute such a massive amount of people in such a short amount of time was only possible because of the local collaboration, which was very active in terms of aiding the Nazis in their program. Case and point is a pogrom carried out by right.wing Lithuanian collaborators in Kaunas as early as June 28, 1941. So, in essence, scale, structure, and the amount of local participation can not be compared when it comes to Soviet deportations and the Holocaust, with the former also not constituting a genocide in the accepted sense both academically as well as legally.

Edit: Fixed a pretty glaring mistake about who supported Pedrin. Thanks to /u/JMBourguet for pointing it out.