The majority of registered Democrats will obviously vote for Harris in the general election, regardless of how she became the party's nominee.
That said, how do we know they're not upset about being deprived the right to choose the nominee? They don't have a bully pulpit to express their feelings like Dem elites do.
I completely agree with what you're saying about the horrors of war and the cowardice of "leaders" who send others to die for their own personal benefit.
However, I don't believe every woman is inherently compassionate and empathetic (Hillary Clinton's position on Iraq and Libya testify to that.) Harris has also vowed to continue funding the wars in Ukraine and Gaza, effectively allowing them to continue indefinitely. The word "ceasefire" is casually tossed around, but there doesn't appear to be a serious commitment to it. Trump isn't any better, as he also wants to continue funding Israel's genocide in Gaza. Vile Iraq War architect Dick Cheney endorsed Harris because he knows she's committed to continuing all of the US-backed wars, while Trump says he will cut off funding for the Ukraine war. Harris is also endorsed by 200 former aides to George W. Bush, Mitt Romney, and John McCain. This pack of neocons wouldn't support Harris if they didn't believe she was the more reliable pro-war candidate.
Of course, people can support whomever they want. If you find Harris optimistic and inspiring, so be it. I just can't see her as anything other than a tool of the establishment. Trump is a vile pig, and I can't bring myself to vote for him either, but the establishment's opposition to him is superficial. He'd occasionally go rogue, and they can't have that.