That's an interesting perspective that I just don't understand, and I would claim that exact opposite is true. Just look at the debate over healthcare. As a group, the democrats created a clear vision for US healthcare reform. At an individual level there's not a clear consensus on what the path forward is, but you can't claim that mainstream D candidates aren't presenting concrete and actionable plans.

Contrast that with the Republican healthcare plans, which consist of nothing more than "not obamacare"

Republicans have the same stance on gun violence and climate change.