Yeah, they badly needed access to the sea.
We are now treading on relative territory. The Czech very much might have stolen Szczecin from Poland in 1920 but the Soviets might say Poland stolen the Molotov-Ribbentrop areas from Ukraine in 1920 too. That is how it works. We are either respecting established borders or not.
Someone mentioned here that Russia has stolen Crimea and might steal Narva but both Narva and Crimea are historically Russian based on the same logic you apply to Szczecin recognizing it as historically Polish although established borders say otherwise.
After WWI these borders were new and confusing, they were imposed upon these peoples by the French and the British.
Besides it was Zaolzie, not Szczecin.