They're readable for very, very simple arguments. Much like very, very simple programs are relatively readable in assembly language. Once one moves on to more

They're readable for very, very simple arguments. Much like very, very simple programs are relatively readable in assembly language. Once one moves on to more complex proofs (which, alas, usually doesn't happen until a "How To Prove It" college course, which is usually taken right after two semesters of calculus), the "two column" writing method becomes untenable.