That's a flag of Latviešu leģions aka Lettische SS-Freiwilligen-Legion. Willingly collaborated with Nazi Germany in WW2.
Sasha, many groups from all around Europe joined the SS. On many occasions people from the same country have found themselves on opposite sides, fighting one another. In many countries there were extremists, either pro-nazi, either pro-soviet and those joined accordingly.
From your answer, it seems that you are trying to justify an invasion by the acts that followed from the invaded part, to justify the cause through pointing at the results.
Concerning the Baltic States, many groups have joined nazis in the hope of liberating their countries fallen as a result of the soviet invadings. Look for example, if you don't like the Baltic states as example, look at Finland. They were considering and tried neutrality until they were invaded by the Soviets. This pushed them on the side of the Nazis.
Except groups of the ones you mentioned when given the example of Latvia, some groups who have joined either nazis or soviets out of ideological conviction, the entire countries have joined either a side or another based on their situation at that time, and except a few, most didn't quite have a real option to not join the specific side.
If not between the nazis and the soviets both invading and trying to conquer as much, perhaps the entire Europe could have rallied, and could have done so on the side of the Soviets if their intentions would have not been from the same breeding as that of the nazis. But then again, we don't know what could have happened if not for the Ribbentrop-Molotov pact - btw, who says that Hitler and Stalin together weren't responsible for starting this war, they should perhaps read the protocol -, we only know what happened, and even if at different levels, the outcome was that everybody started killing everybody.