We lose more hands with soft doubles against 2,3,4,5,6 than when we don’t double.
We lose more hands with hard doubles against 7,8,9,10 than when we don’t double.

We make more money by doubling, even by winning fewer hands, because the sum total of our wins versus losses exceeds the value of our wins when we don’t double.

I erroneously stated that we won more hands in higher counts by doubling and splitting. 21forme made a valid po8n5 on defensive splits, citing that we are still overall losers, but that we lose less.