If you didn't say anything about Obama pardoning Manning but are upset Trump pardoned Arpaio you might be alt left— Jack Posobiec 🇺🇸 (@JackPosobiec) August 26, 2017
Chelsea Manning wasn't pardoned. Manning pleaded guilty and served over 6 years in prison before her sentence was commuted. Manning's felony criminal record stands, along with the attendant consequences of a felony criminal record.
The considerations behind pardons and sentence commutations tend to be idiosyncratic, so direct comparisons have limitations, but a better comparison with Arpaio would be whether one approved of Bill Clinton's pardon of Marc Rich.