Yes, we went through this with Eric Garner
Unless the cop's life is in danger, in which case any lethal force is allowed. But even then, the methods of subduing a suspect that are taught don't include suffocation.
Well, if they are trained as such and still do it, the entire training (or more accurately - screening) is questionable.
In my line of business, there's ethics training and oversight. But the bottom line is that there are certain things that are either part of you, or they aren't.
Robust and extensive screening of personality and character is probably the most important thing missing. It seems like jurors are disqualified faster than people are rejected from the ranks of law enforcement in this country.