The point is that it's nothing but a deflection tactic, and I don't believe the people doing the lynching were typically the same people concerned about human rights abuses in the USSR. It's an oversimplification used to prevent discussion about real problems.

I think there is a valid point to it – there is a certain degree of hypocrisy in criticising other country's human rights problems when you aren't doing enough to resolve your own country's human rights problems. Calling it "Whataboutism" seems to excuse that hypocrisy rather than giving it the condemnation it deserves.

I'm not defending the Soviet Union, which was truly a horrible regime.

What I'm saying, is the proper response to a criticism of lynching, is to agree with the criticism, not argue that the crimes (no matter how horrid) of those who are making the criticism renders the criticism invalid.

Agreed. You're right, it is hypocritical. There was fierce fighting between two sides of the civil rights issue during that time though. We weren't doing enough, but many people were trying.