It's not about the money (for me, though it may be for some).
It's about the startlingly remote possibility of background checks actually leading to a meaningful improvement in child safety.
It's about the fear-mongering that is encouraged by requiring background checks, which is belied by current research into crime rates and patterns.
It's about the invasion of privacy that is being imposed. Yes, the data is public data. But turning the keys to personal data over to school administration is an intrusion into one's privacy - otherwise, the school would just run background checks on everyone, without waiting for their consent, and just roll it into the school fees.
It's about the incredibly poor quality of the data upon which these background checks are based, and the poorly trained individuals who interpret the data that is returned, frequently incorrectly.
It's about the presumptions of guilt, whereby parents whose poorly-maintained and/or interpreted data raises a "red flag" must prove their innocence, rather than those wishing to restrict their access to a public accomodation being obligated to prove their guilt.
It's about inappropriate presumptions of future guilt, where individuals have completed court imposed sentences and/or treatment, but continue to be "punished" (and I will even reluctantly concede that sexual offenses might need to be treated differently here, but presumptions of future guilt with regard to non-sexual offenses are particularly troubling).
It's about the manner in which schools and vigilante watchdog groups turn individuals into societal pariahs, without bothering to confirm the validity of data or inquire into circumstances.