Single-issue voting is something I consider a very large threat to the democratic process in the US, and is also something that both parties have become exceedingly good at creating in the elctorate.

The reason I consider it a threat is that it allows either party to meta-game the fact that many voters can be persuaded to vote against their own interests.

How could any decision that voters make about how to cast their votes be a threat to the democratic process? A voter grounding their decision about who to vote for on a single issue is democracy working as intended. If this is bad it's only bad in the sense that voters in a democracy can vote for bad people or policies - but this is not something democracy as a system does or can promise to avoid.