Intuitively, fines should deter unwanted behavior. But, in many ways it inadvertently legitimizes it. In behavioral economics, they've shown that when day-care centers fine parents for being late to pick up their kids, more parents come late. In effect, the parents view the fine as the price for being late.
For fines to be effective, they need them to be large enough to feel painful. Otherwise, they just give people ideas about what will be tolerated. By implying that you expect others to engage in this behavior, you've added another viable option to their decision-making.
Unfortunately, the unintended consequences of introducing fines to a system may be hard to shake, even if the fine is eventually repealed. So, try to address the root causes for the undesired behavior directly and only resort to fines if you can't find other solutions.