Discord is proprietary software. You don't know who wrote the code, what the code is, what it does nor how it does it. Their servers run proprietary software as well, which means for all we know they could be listening in on every conversation that is spoke. Plus, discord isn't end to end encrypted and funded by a Chinese company.
* Proprietary software, you don't know what it does nor can you
* The servers could listen in on everything you say, due to the lack of end to end encryption and proprietary server software
* Essentially owned by the Chinese ("do X or we'll cut your funding!")