Regardless of whether or not you provide your own SSL certificates, cloudflare still uses their own between their servers and client browsers. So any SSL encrypted traffic is unencrypted at their end before being re-encrypted with your certificate. How can such an entity be trusted?
To clarify, I did not mean MITM attack. It actually wouldn’t make sense to say that cloudflare is a man in the middle attack, since it is a company and not an action.
I didn’t include the word “attack” anywhere.
MITM is commonly used together with attack, so your misunderstanding is understandable. However the acronym just stands for Man In The Middle, which is why it is followed by “attack” in such situations.