The Spanish Civil War found Stalin's forces more closely aligned with the Western democracies in that struggle against the Nazis. Why that situation would incline Stalin to make pact with Germany is not clear to me.
It is my understanding that rather than Molotov flying to the West, Ribbentrop flew to Berlin while the emissaries of France and Great Britain were taking a slow boat to St. Petersburg and so they missed that date with destiny when Molotov stole the march on them.
I do not understand why Britannica would necessarily be biased in favor of putting Great Britain in a bad light? Anyway, there are several sources for this view, Kissinger to the contrary notwithstanding.
If Stalin was well aware of Hitler's aggressive designs against Russia, why would that impel him to make the pact? He made the pact in spite of that knowledge because he had so little respect for the Western powers, as I noted in my first reply and with which you seem to take issue.
Finally, there is a great controversy about whether Stalin actually apprehended the danger from Germany at least that the danger was imminent. Additionally, Stalin, if he apprehended the full dimension of the threat from Germany, needed more buffer space between him and Germany which the pact provided him.
