More specifically, it's flagging the domain we use to serve images from as suspicious.
It's not.
Stop using McAfee, it's terrible, and it's literally hijacking your connection in this case.
EDIT: Copying and pasting my longer explanation;
A message specifically for Americans on Comcast/Verizon/CenturyLink;
If you're getting an error message about your connection not being private, or that Mangadex has an incorrect security certificate, or a big McAfee page coming up when you try to access the site, read on.
McAfee is MITMing you and attaching their certificate, so Chrome (correctly) thinks there's an attacker intercepting your connection, and warns you. Nothing to do with us, fuckall we can do it about it.
Turn off McAfee, it's either on your device, your ISP's router or somewhere buried in your ISP's settings. Comcast, Verizon and CenturyLink all appear to be doing this.