Good typography is about making the correct decisions regarding your text. If justification is making a passage hard to read then it's simply bad typography and doesn't mean justification is bad as a concept. Ragged-right isn't necessarily going to save you from rivers either although they are far less likely due to uniform spacing.
Oh, I know. I hate them as separate entities. I'm not even convinced necessarily that justified text causes more rivers - they make awkward gaps and ruin my pace, but I don't usually get distracted by rivers with justified text.
Justification without gaps works best with aggressive hyphenation. If the hyphenation isn't good, the text is full of surprises at line wraps. It's hard to do justification well as a result. It's usually restricted to newspapers with limited space these days.
> It's usually restricted to newspapers with limited space these days
That's false. Almost any printed publication uses justification and hyphenation by default: books, magazines, scientific papers. The big exception is websites.
They usually do cause more rivers simply because on many lines the spaces are significantly larger. Since you only would letterspace as an absolute last resort (and probably not even then), it tends to create more dangerous whitespace per line.
