First and foremost, a massive communications failure, and possibly an error in navigation. From the article, it seems that the responding officers weren't even sure they were at the correct objective up until the point of no return. Could the homeowners have made better tactical decision? Sure. But in the end, they were reacting to a situation that they should have never been forced into, and I bet they were scared beyond belief the whole time. An unmitigated rush to catastrophe. This led to a shooting that was fatal to a citizen in his own home. Total mission failure, and I have no idea if the actual domestic call was even addressed, or how it may have ended- was another victim injured or worse while a random homeowner was being shot to death? A weapon discharged is a bell that can never be un-rung. If something comes out the end of your gun, you own the responsibility for it, for better or worse. Serve and protect.
The police got dispatched to a hot call. There is urgency in those types of calls to get there as quickly as possible. They knocked on the door to ascertain if they were at the right location as many houses are poorly marked and have no clearly displayed number. Sometimes the callers themselves aren't even sure of the correct number. Once they began knocking they also identified themselves. They didn't try to make forcible entry.
If they had been serving a no knock warrant then I'd agree with you, but in this case the police did what they are supposed to do. It's not their fault they had a gun pulled on them. I plaxe the blame entirely on the homeowner who made a catastrophic mistake.