My rule of thumb is "the less I'd like to do a job, the more the person doing it should be paid."

That does already put upward pressure on the wage. Same reason that graveyard shifts tend to pay more than first or second shift positions of the same job, and that more dangerous jobs tend to pay more than safer ones of equal overall difficulty.

so-called unskilled jobs

"Unskilled" is not an insult when talking about jobs, it's just terminology/jargon. In this context, it describes a certain category of job: one that requires no prior special certification or schooling to be qualified for, and that the typical person can be trained to do to a satisfactory level within a month or so.

jobs that get routinely exploited.

The fact that many people are qualified to do those jobs (due to their low requirements) is the primary thing driving the wage down for them. As long as there is someone willing to do the job for X amount less than you're willing to, they'll get hired over you, because the job is such that individual excellence doesn't make nearly as much difference. You can't really blame the company for hiring the cheapest adequate labor they have access to, they're doing no different than the workers trying to find the highest paying job they can. To criticize one without criticizing the other is a double standard.