You definitely need evidence, so reference and link articles and statistics in your response.
I think you should talk about these 5 different arguments, many of which you had in your original letter but maybe could be expanded upon:
1. Evironmental- both the energy required and fossil fuels and also the effect on ecosystems, birds, ect.
2. Economic- the hundreds of thousands of $ being spent on these lights could be used by actually putting up security cameras or something which directly reduces crime.
3. Human health and mental health- cite articles that have researched the effects both on the mind and body.
4. Impact on science- us astronomers are actually a large impact, we conduct research such as exoplanet photometry, spectroscopy, and other things. This light pollution directly impacts astronomical research.
5. The real impact on safety- that 97% positive response is from a population largely ignorant about the real safety imact. As some of us have mentioned, it is actually the other way around, burglars will not rob a house if they can't see, thus the decrease of crime when it is dark. In fact, I would be willing to bet that the 3% negative response is from the people who actually did research.
I hope this helps.