I hope by "obvious reasons," you mean illegal, because it most probably is. Laws vary from country to country, but I am almost certain that using somebody else's address without permission from the resident is illegal in so many countries.
Yes, that's one of the reasons.
And I assume that you'd also be using the name of the person living in that address since, well, you're keeping your identity unknown. This is worse. Although you're not using his/her name for any fraudulent purposes, I suppose this still falls under identity theft.
That actually happens quite a lot here: someone orders something online, but at someone else's address. After delivery, they just go there and say they made a mistake with the house number. Many webshops allow you to pay later, and the receiving address will get the bill.
I think I'd better ask for permission.
You can't be anonymous if you ask permission.