When planning my releases, I break down Initiatives into Features etc. These Initiatives and Features will have multiple Stories (ie Backoog Items) that might span several Release/PIs and Sprints. I drag/drop my Stories into Sprints.

This is all well and good... Very agile like.

But why when I am working in the Roadmap view must I manually set start/end dates??

This is duplicate data entry and will most certainly result in data inconsistencies. If I change a start/end date on a planning item in the Roadmap view, how would all of the downstream users be notified that any child items of that PI are now beholden to new start/end dates? Are there any errors alerted if these new dates violate any sprint dates?

Can't we rather have the start/end dates for planning items default to the soonest start and latest end dates of any sprints which contain any child backlog items?

If I take a backlog item out of one sprint and move it to another sprint, update the dates of the parent item?

I HATE HATE HATE duplicate data entry and the obvious consistency errors that result.