"Because it was illegal,"

We discussed the legality early on.
Most expert opinion was that it WAS legal.
Nothing against that from UN, The Hague or even Pakistan.

" it sets a very dangerous precedent,"
Yes. Perhaps it will deter some future terrorists.

" it effectively says that if the world's biggest superpower can ignore protocols like informing a country that it is about to launch an attack on a specific target within its territory,"
Obama was at pains to justify that.

"that the aim was clearly to kill, not to capture,"

That is not clear at all.

" that no regard was taken of any other casualties in the raid,"

Obama must have been tempted to just bomb the compound and kill everyone.
Had the Seals suffered heavy casualties, or the raid degenerated into a Jimmy Carter style fiasco, he would have been very politically damaged.
A brave decision I think.

" that the body was illegally disposed of"
Yes, but as with the whole situation, it was by far the lesser of evils.