Maybe this will help me understand where you are coming from.
Can you describe a situation where a simple knock to serve would be acceptable?
At what point, in your mind, is the threshold for allowing no knock warrants?
Also, for reference:
Amendment IV
The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.
Remember, the probable cause came word of mouth from a CI, and the property to be sieved was black tar heroin and a semi auto 9mm, neither of which was found.
The police had valid warrant and they weren't required to knock.
Why shouldn't have they have to knock? Because violent criminals would ambush officers if they had. Is that really hard to understand?