It's a seldom-acknowledged fact but ad hominems run both ways.

If saying that he can't have been that good for his bad actions is an ad hominem, then saying he can't have been that bad for his good actions is surely also an ad hominem.

For however we define good and bad.

I think it's quite healthy to be able to discuss say, a person's legacy, from different angles rather than restrict discussion to only the good parts.