A boisterous crowd of a thousand or so packed the Stanley Marketplace in Aurora on Sunday to hear a White House pitch from Robert F. Kennedy Jr. — a presidential candidate who isn’t yet on Colorado’s November ballot but who said he represents an opportunity for people to “vote out of hope and inspiration” rather than fear. Kennedy started his speech by decrying his omission from two recently scheduled presidential debates, noting that independent voters are by far the largest bloc of the American electorate.