Trust me, I understand their plight, but children don't answer, "telemarketer" when someone asks them what they want to be when they grow up. If these jobs were gone, some other low-paying exploitative industry looking for unskilled labor would fill the gap.
I'm not proud to admit it, but about two decades ago I worked for a couple companies involved in telemarketing, so I met many telemarketers and worked with them fairly closely. They don't love their jobs, most barely endure them. They did it because it didn't involve a hot fryer and paid a dollar or two more. Some were just working their way through school. Nobody planned to keep doing it long-term. The big one that did a lot of outsourced telemarketing was shifting toward being a more general-purpose call center, followed by a tech support center after they moved the lower-paying and less-skilled jobs to poorer locales (MO and GA, were major targets at the time.) where desperate people were easier to find and had fewer options.
Not to take away from the argument that people depend on this income, which I fully understand, I'm surprised that you (or anyone) would defend the industry at all. It is exceptional in the way it races for the bottom, exploits vulnerable people (both employees and "customers"), exploits infrastructure (government- and ILEC-subsidized, often using tricks to get huge kickbacks), and aims to exploit various state laws (ex: right-to-work, low minimum wages, "training" loopholes, etc). Short of MLM, high-interest unsecured loans, and tobacco, I can't think of another industry that is more harmful to poor people.