> inhibit the [...] RNA polymerase of the [..] virus
If it would just simply stop RNA synthesis (eg. inhibit any RNA-polymerase) or if it would actually break RNA in general, it would kill HUMANS just as well!
The point of antiviral compounds is to selectively inhibit/kill mechanisms/components of the virus and not the human host... there's hundreds of thousands of antiviral and antibiotic compounds that are not very useful because they'd kill humans just as well or give them horrible cancers or god knows what else...
As the saying goes... "Everything should be made as simple as possible, but not simpler."
