Thomas didn't issue a scathing dissent against voting rights. It sounds like you didn't read what he wrote if that's what you think.
He wrote a scathing dissent against what he presents as legally and logically flawed arguments laid out in the majority opinion.
Thomas isn't against voting rights here. In fact, his dissent holds the Court to the VRA. He is against the position of the majority that runs *counter* to the Voting Rights Act.