I'm conflicted.
On the one hand, including Joe could potentially help him adjust to the world, and provides him with the opportunity to observe what good behavior and self-control look like. Also, including Joe helps other kids realize that the world is full of all kinds of people, and hopefully they develop empathy and kindness towards all the Joes out there, by seeing them as people, by getting to know them a little. And including Joe helps his family get some precious time away from him, because with a child that demanding it's hard to do errands, clean the house, take care of other kids, etc.
On the other hand, Joe is disruptive to the learning process and the classroom environment. The class is not free to put their heads into books without constantly surveilling the room, and Joe. The teacher puts extra time into creating a plan in case Joe erupts in violence. And this isn't potential violence that teachers plan for but don't expect to happen (a gun threat, a tornado) - this is real, everyday, "yes-its-going-to-happen", definite stuff.
On the other hand (yes, I realize I now have listed three hands - I only have two in real life, but in this case I need another), at any time, our kids could be exposed to danger. Its not just Joe that we have to worry about, it's Steven and Justin and Samantha and Lily-Ann, and that teacher that got fired last semester, and a parent who's infuriated that his or her precious snowflake didn't get an A+ in every class, even though Snowflake didn't do the required work or study for tests who could snap at any minute. So, inclusion or not, its a sad reality that being in this world always can bring danger. Maybe having Joe in class helps the other students and the teacher be more vigilant in general? Maybe Joe will help someone develop an awareness of mental health issues. Just think about how many news stories we hear where the neighbors say "he was the nicest man; I never would have thought that he could do this". Its sad but real.
On the other hand (I know, that's 4), some school staff have to endure parents who demand that their child be included, even though it's not a good idea. Some parents threaten with lawsuits and refuse to be reasonable. Sometimes the school's hands are tied and they just have to make a place for Joe. And then, some parents are desperate. There is no place for Joe and they have nowhere to turn. I have a nephew whose parents are well-educated and financially secure. However, the nephew is bipolar, and he OD'd and survived but he had a stroke as a result. His behavior is much like Joe's, except he's about 25. He needs constant supervision, and should be in a group home, but all the calls they have made have turned up nothing. There are homes for all kinds of conditions and diagnoses, but not for his combination of conditions. They're getting desperate. We need more access to care options in this country, more help for mental illness, and more resources. My nephew's parents have all the time and money to find him a place but instead, they live in fear in their home, wondering when he will have another manic episode. Its the Joes in this country who need a better way to get educated and stay safe and grow to be the best person that they can be.
I think you're doing the right thing. You're helping your daughter be safe and aware, not disparaging Joe, and not sheltering your daughter in a closet at home. But I would perhaps have a Plan B in the back of your mind - if Joe's behavior deteriorates, if your daughter feels too uncomfortable, if the school isn't appropriately managing things, if the education starts to take second place to just tiptoeing around Joe, what would you do? Is there a private school, online public schools, homeschool, or a different school in your district that maybe might be an option? Stay calm, document events, consider a Plan B, and encourage your daughter to be careful without being scared. Give her permission to leave the room if she has to, if Joe is choking people or throwing things.