Because it discriminates a marginalized group which is by tradition very important to the FOSS community: students
Also, no it wouldn't kill spam. The spam would be moved to pwned machines where the owner would suddenly have an incentive (financial) to fix the system, if they know.
What remains is people who would be so rich that $1 means nothing to them. Ie. white collar criminals who are already rich enough to not care.
A $1 fee is fine for Indian software developers and it kills the spam. If it's a greater burden for people in India than the US, well, not all solutions are perfect, but some are useful.