>> the reasoning that we shouldn't use the free license plates because they're reducing the number of jobs making them doesn't make sense.
Yes, once the things are made, simply wasting the things on principle is, well, simply wasteful.
That said, if that step of wasting them is required in order to stop the practice of (near-)slavery, then the waste could be worthwhile.
Either way, slavery is bad both in it's own right and to the extent that it harms wider society by degrading the value of others' labor.
This could also be solved by requiring all jobs to pay a bona-fide living wage, as in, you cannot hire anyone unless you are paying them for 40 hours of work an amount that is sufficient to support them and dependents for all basic needs, i.e., food, housing, health, transport, etc. Perhaps an exception for dependents who are entering the workforce, who could be paid lower rates for a certain time. With this, then slavery wouldn't have so much outside harm in addition to its intrinsic harm.