You're right, from one observation of a redshift and nothing else you can't deduce much. But there is the relationship between brightness and redshift which is difficult to explain, and also all the effects that go into the correct prediction of the Cosmic Microwave background such as the Sachs Wolfe effect make no sense if space doesn't expand.
The fool hath said in his heart, There is a God. They are corrupt, they have done abominable works, there is none that doeth good.
Psalm 14, KJV revised edition
