Demonstrating causality would be doing more work than is necessary. To argue against the hypothesis that the values of A, B, C, ... are all increasing, you don't need to show that an increase in the value of A leads to decreases in any of B, C, ...; you just need to demonstrate that the value of at least one of A, B, C, ... is not increasing.

(To avert the negative connotations the above paragraph would likely otherwise have: no, I don't think the decline of lynching caused those various ills.)