Did it occur to you that then people will focus on reporting?
I think that's the point.
The more people start reporting worthless spam posts, the more will be deleted.
And more spam being deleted means people will actually focus on not spamming this forum for a few cents.
Many will report posts that maybe don't need to be reported.
It'll just create another problem imho.
I don't think that would be a huge issue.
From the report-page:
Do not worry about your accuracy too much; one accurate report is worth many inaccurate reports.
The badges would be for good reports. Reporting 100 posts which shouldn't be reported will not get anyone closer to a badge.
And then the reporting behavior might be changed.
But another requirement for the badges could also fix this potential problem.
Combine a minimum amount of good reports with a minimum amount of accuracy. Then people won't start reporting hundreds of posts just to get a few good ones out of it.