-Overthrown Gaddafi and destabilized Libya in the process, leading to million of small arms washing into the Sahel. Jihadists groups have killed hundreds of thousands with those weapons, further destabilizing the region.
-Funded and backed murderous dictators like Hissene Habre who tortured, killed, and raped roughly 40k innocent Chadians.
-Other dictators that have held unto power with implicit/explicit American support include Mobutu, Amin, Barre, etc., and I'm not going to go into the atrocities they've committed.
-Continue to meddle in African countries, including their implicit support for the overthrow of popularly-elected governments like Egypt's Muhammad Morsi, and Congo's Lumumba, after which the country fell apart .
These are just a few examples off the top of my head. No matter how much you scaremonger about China, all they do is transfer technology, build infrastructure, and assist with explicit approval of local governments.
Do they have evil intent in the long-run? Who knows?
But, given their track record so far (of going heads down and building stuff) and the West's history of plain maliciousness, it'd be stupid to suggest anyone shouldn't partner with China.