When we first started using pesticides we didn't understand the long term implications. How can you be so confident that you understand the long term implications of an arguably much more complex application (genetic vs chemical)?
However, the active ingredient, double-stranded RNA, is ubiquitous in nature without obvious adverse impacts. It degrades very readily. It doesn't impact gene expression in mammals, even if completely homologous to a transcript (which is why in contrast to synthetic short interfering RNAs there's no obvious use as a therapeutic). It's an extraordinarily narrow spectrum approach, which is quite different to anything in the past, and why the approach is receiving a lot of interest and investment.
There's ongoing synthesis of data on environmental impacts. Have a read: https://www.oecd.org/officialdocuments/publicdisplaydocument...