Earlier quoted context omitted.
Computer Modern is a hideous font. It's particularly terrible when rendered in Postscript/PDF, which is how almost all documents produced with it actually get read. But the +10 credibility is absolutely true. It's like CS grunge style: when you wear ugly clothes, you look more authentic.
How is Computer Modern much worse than, say, Times New Roman?
These characteristics of the font are intentional: it's really a showcase for Knuth's Metafont system which lets you tweak stroke contrast to a high level, so you can create many weight and casing variations of Computer Modern parametrically. And it does look bearable in print. But it's really the worst possible screen font.
Times is much better in this respect because it was designed for readability long before computers, for newspaper printing where unexpected ink bleed and other artifacts were daily routine.
(Cynically, it's possible to view Computer Modern as a fitting portrait of computer science itself: the font is used because it's exciting to have 62 tweakable parameters in a system designed by someone famous in the field, not because it's any good for the end users.)