Alright, let's cut to the chase: yukkuri are retarded beings with low intelligence, and yet they bear the facade of intellect by using human speech, so they don't deserve happiness in the slightest.
The problem is that while yukkuris speak the human tongue, they do not have the intelligence to comprehend the modern and civilized human culture, its etiquette, constraints, typical/desired behaviors and forbidden actions, nor do the typical yukkuri have the ability to articulate its ideas into ways that are socially acceptable and tactful. As a result, they communicate on the same frequency as humans, yet do not have the means to restraint their instinctive urges from oozing out in their speeches and actions.
Just a simple example, have you ever seen a yukkuri say "please"? (in translations. If you want to be savvy, read through the raw text and look for places where they actually say "kudasai" instead of the usual imperative/casual "-te ne" forms). I sure as hell haven't seen more than a quarter of a dozen occasions of that. Another thing, I'm sure you have never seen a sober and conscious person shitting in public and never will, but what about yukkuris? These things, bearing the facade of the complex linguistic ability of humans, would most likely shit anywhere, anytime they want, including cases in the presence of others of their kind. And they never feel ashamed about it - instead, they must always broadcast to the world about their holy poo-poo time. Even their public toilets - simple shitting holes to be exact - do not possess any kinds of cover to conceal its users, not even simple leaves to hide them. And then there's @Canttakeiteasy 's argument about koyukkuri's supposed superiority to newborn children. Well they can speak from the moment they were born, but what is the point if they cannot even control the urges that they spout out? What is the point if they cannot understand their social standing to appropriate their speech, and will talk smack to just about anything they face? Now, I'm not saying that (newborn) children are any different, but stating that newborn yukkuri are superior merely because they can speak is just bogus. There's a saying that reflects my point: "Even a child can easily speak, but learning how to speak properly can take a lifetime."
Speaking the human tongue doesn't automatically give yukkuris any worth, it only subjects them to the scrutiny of cultures that they cannot possibly fit in. They tuned into humans' communication frequency, but do not have the intelligence to be qualified for it. Thusly, their barbaric ways when broadcasted onto the human channel would only justify each and every single retribution that falls on their heads, and strip them of any and all rights and happiness that they could've had. Their reputation of obnoxiousness, violence, childishness, stupidity, and lack of restraint only came into existence when their low intelligence (downright retardedness) caused these traits to be exposed through speech, and are caught on the human cultural radar. Had they remained in the realm of animals and mess around among themselves, they wouldn't have been brutalized so much. "With great power, comes great responsibilities" - when yukkuris harnessed the ability of speech but not the intelligence to understand the human ways, they've signed their own death warrant. And I'm more than happy to strip them of any and all things they may hold dear.