Student Loans Ramble

A few months ago, in May, there was an article in the NYTimes about student loan debt. It talks about some ways in which the schools and lenders work together, or dysfunction together, and wind up with a system that can be predatory and exploitive and ultimately repressive to people on the down side of it.
But I think it also comes with a punch line:

"The balance on [her] loans is about $97,000"
"She recently received a raise and now makes $22 an hour working for a photographer. It’s the highest salary she’s earned since graduating with an interdisciplinary degree in religious and women’s studies."

I'd like to be respectful to my friend with an advanced degree in religious and women's studies, but in retrospect in this case this seems like an obviously bad idea. The article draws some parallels to the real estate bubble. People getting loans they can't afford because they assume what they're buying will be worth enough to make it all better in the end. It didn't work in lots of inflated housing markets, and it didn't work out for this young woman's education. That $100000 education (which will cost a total over $200000 over the life of its interest payments) didn't wind up being worth much.
Is there some kind of rule of thumb about this? Business math? I want something short like "Don't buy an education that won't buy you a job that can pay it back in less than N years." or "Don't pay more in tuition than K*expected_salary." N in 5..15? K in 2..4?

Here's a pretty graphic indicting the industry and the laws they've lobbied for

I'm seriously considering this rally thing

And now I'm thinking about designing a sign to carry. In the sense that the whole system is mad and needs fixing, I could vie for either of my favorite system reforms: impartial redistricting and rankings ballot voting.

Should I:
A) Make a sign with one side each
B) all voting
C) all redistricting
D) not make a sign, signs are dumb