For me it would be "It depends." It would depend on the amount, the person's age, their own earning potential, and how aggressively they're working to pay it off themselves. For example, I wouldn't jump into paying a $200,000 SL debt for someone with a liberal arts degree from a private school, that is earning $30,000 a year as a social worker and saving little because of their spending habits. But then again, I'd likely not marry someone in the first place with that kind of (or lack of) financial sense.
But, if it was reasonable debt and the person was earning and working aggressively to pay it off, then it could make sense to work as a couple to pay it off and free yourselves from debt to do bigger/better things. For any significant amount, it would be a good idea to put something in writing that if the marriage ends, the debt paid by the other person is credited for that amount in any split of assets (i.e., they get their money back). This advice comes from someone who lost $700k in a divorce with no prenuptial agreement.