There is a lot of research on this. It's a deep, fascinating rabbit hole and I don't know its contours well enough to flag the entrances. But it touches subjects like mammalian postpartum depression, infanticide in great apes, why the characters :) make one go "aww," cute aggression and a host of other matters.
To address your point a bit more head on, I imagine public reactions to a publicly-defecating child would be very different from those to an adult.
Are you so out of touch with basic human desires that you don't see the difference between having _your biological baby with your genes_ and a random homeless person? That people love their baby _despite_ their poop, because of the joy they bring, and because it satisfies the most primary of biological drives (reproduction).
And you think it's weird that I'm okay with my baby's poop and not the poop of a random adult.
I've admitted that I don't like homeless people, but I put forth an authentic point of view and my engagement is a form of earnest attempt at solving the problem despite my personal dislike. I've noted the types of things I would be willing to vote for and what is less likely to win me over.
What do you think you are adding to the situation? You put on this position of caring so much about the homeless population yet all you seem capable of is burning bridges for nothing in return.
And despite your implication, it's actually not controversial to have the opinion that people generally care more about genetic heirs than adopted ones. God bless those with enough patience, understanding, and resources to adopt, but there's a reason why 99.9% of people on Earth have their own babies. Or are we just cretins in your view?
Maybe rather than caring so much about the quality of discourse online, you should look into those feelings. Damn.
Oxytocin--the hormone critically involved in empathy and social behaviors--has been linked to toxin-elicited and socially-mediated disgust [1]. If that link holds, it suggests why public defecation is the emerging turning point of the debate.
Rhetorically, this means trivializing the problem is unlikely to be successful. People will lose empathy for people who shit on their street. On the flip side, this offers a well-scoped beachhead. Solving the public defecation problem could rebuild empathy for San Francisco's homeless and give political oxygen to the broader, more-intractable problem of homelessness overall.
(I'm honestly shocked nobody has run for office in San Francisco on a vision zero-esque pledge to eliminate public defecation.)
[1] https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/gbb.12...