The entire world is always looking for easier and more efficient methods of doing work. I don't think that's an invalid argument at all. It's the professor's job, yes - and why can't they seek out "better" methods of doing their jobs? (I use quotes to suggest that 'better' is subjective.)
Is there an argument against these tools that says they're ineffective? That says they make professors less effective? Maybe, but that's not the same as "...makes it easier ... is a stupid argument..."
In my experience the online assessment solutions offered by most commercial publishers are horrible, while open source solutions like WeBWorK http://webwork.maa.org/wiki/Get_WeBWorK and MyOpenMath https://www.myopenmath.com/index.php are not bad and have been around for many years.
Yes they are not as "shiny" as the commercial offerings, but I'd trust them much more for actual learning/practice/quizzing than the mainstream publisher crap.
The argument is that it makes it easier for the professors/teachers to grade homework when they're submitted electronically. Of course, that's a stupid argument since part of a professor's job is teaching students, and that inevitably involves grading things. Few professors would be convinced by such an argument though.