This is true. It's also 'whataboutery'. Slavery was always abhorrent, and the fact it was and is widely practiced does not excuse its beneficiaries. What is interesting is that I don't think you are deploying this rhetorical trick as a means to persuade others, so much as to make yourself feel better about something: to assuage some sort of cognitive unease. Contrast this with the author of the article: she owns it. That is absolute moral bravery.