"When you surround an army, leave an outlet free. Do not press a desperate foe too hard." -Sun Tzu You should allow your opposition to at least believe they have an alternative to digging in and fighting you to the bitter end. Even if you have no intention of allowing them to escape or surrender, you should let them believe it's still possible.
There was an alternative though. The alternative was for this guy to not make a cringy blog post about his past anti-semitism, and simply not talk about it.
The solution to people having horrible ideas in the past, is not for them to make giant, public renouncements.
Instead, the solution is for those people to be ashamed enough about their past positions, that they won't even admit that they held them.
That is a really good solution for most people, as most people are not going to have every little detail of their past interrogated. It is very much possible for people with these bad ideas, to merely stop having those bad ideas, pretend like they never had them, and join productive society.