The thing is, it's neither "bad" nor "good", it's just history. And in that context, the Janissaries are quite an interesting case because their history is filled with very extreme ups and downs.
> "Beyond ‘slave soldiers’" "Essentially, they displayed their ‘slave’ status with pride" --- oh, that makes it OK then?
If you'd read the whole Wiki article, instead of just quoting the passages that support your notion, you'd also realized that their position immensely changed over the centuries.
Yes, they started out as a "slave soldier" unit in the thousands, made up of forced converts. But their efficiency on the battlefield quickly made them a very renowned unit, so renowned that over time even Muslim families tried to get their children to be recruited.
This went on for a while until the Janissaries became such a powerful institution that they dominated the Ottoman government and could literally dethrone the Sultan, which they actually did, even killing Osman II in 1622.
Until in 1826, after centuries of Janissaries running wild, the Sultan Mahmud II decided "enough is enough" and "disbanded" the Janissaries corps in what is nowadays known as the Auspicious Incident [0].
So, while they started out as a forced conversion soldier group, they ultimately turned into something very different. Heck, I'd like to think them destabilizing the Ottoman empire like they did, was their form of revenge.