Regarding the first issue, as a fundamental legal and policy matter, "no-knock" warrants and excessive force in the execution of a warrant are bad things for the reasons you mention (4th Am. and public safety), and another: officer safety. If someone comes through my door suddenly and violently, I would attempt to forcefully defend myself. This is a recipe for disaster, not to mention broader negative effects on society from institutionalization of the practice.
And regarding the second issue, I agree that if there was not just cause for the force used, a serious and fundamental abuse of rights occurred. However, I wouldn't go so far as to say it's a "clear" case of anything without knowing all of the facts, which we do not. It seems others here may know more about this than what was in the newscast (I don't), BUT watching the newscast, the only evidence that this was the case was a broken door, and the statements of the person interviewed. If, as the person on camera said, the agents broke down the door without giving him the opportunity to even get out of bed and answer their knock (or if they didn't knock and announce at all), someone should be held accountable. Clearly, totally improper. No question about it.
BUT, bear in mind that even when executing a SW in a non-violent matter, LE may force a door if the occupant of the premises to be searched does not answer after a reasonable lapse of time, if he answers and refuses to permit entry, or if they believe evidence is being destroyed. Is it possible they knocked multiple times over the coursel of several minutes, and loudly announced their presence? Is it possible they saw curtains being drawn inside the house and knew someone was inside and was not answering despite their attempts? Is it possible that looking through a window they saw this individual in the process of destroying documents? And how do WE know that he wasn't a subject of the investigation -- we only have his statement that they were looking for his ex-wife. On its face, the newscast paints a convincing picture of governmental over-reach. All I'm saying is it is possible circumstances exist, yet unknown, which justify the forced entry and that individual's detention during the execution of the warrant.