In fairness to France and the USSR, had Britain and Poland given the go ahead in 1938, the french army and the red army would have been pouring in Germany. It was Britain selling out France's allies. With Poland happily taking Hitler's tablescraps in 1938.
It's a fair point, and we may be at a chicken/egg sort or impasse, but if France is allowing for Czechoslovak dismemberment, why wouldn't Poland participate?