I think both of their arguments are inherently flawed
1) you'll be able to make bigger monthly payments. In a vacuum this is true, but it comes at the expense of saving more money. If there is any 401(k) match at all this works out to a no-win proposition even if the market drops considerably.
2) you'll be extra motivated to pay off your student loan debt. The reasoning here is pretty flawed too. Behavioral economics has shown that we miss money less if it never enters our bank account, which is why 401(k) payments can be so great - that money typically gets deducted from the paycheck. Student loans, OTOH, are paid out seperately, which means a person sees that money enter the account, and then quickly leave the account. Also, "motivation" is a pretty strange justification. You're pretty much required to make monthly payments, just as you are with your cable or electric bill. Unlike credit card bills, the standard SL bill has a set payback period (usually 10 years) Sure, you could default, but a person who's defaulting on their loan isn't likely to be someone who's also putting away thousands into a 401(k).
As NoStacheOhio indicated, the only time it might make sense (or be "less bad") is when you can pay off the entire loans in a very short time period - like within a year or two and if there's no company match.
