I'm from the southern US, which is historically more conservative than the rest of the country. I'm not in any way claiming that the following viewpoints are universal and accepted in this region, but a large enough portion of the population holds these viewpoints, preventing further progress:
1) Anyone who gets shot by cops must have done something to warrant being shot. Even for people who get shot during traffic stops, that person did something to get pulled over in the first place. If they had a criminal record in the past, even if they didn't commit an offense during the situation where they were killed, there's a good chance they would have offended again, and this preemptive killing probably prevented a future crime.
2) In the case of this swatting incident, the blame lies 100% on the person who made the false police report. No false report, no shooting. The cop had reason to believe based on the report that the man who emerged from the door claimed to have a gun and had killed in the last hour, so it was plausible to believe he may try to retaliate and the appropriate force was used. No time for fact checking during an active shooter situation. "Shoot first, ask questions later" is considered an appropriate way for the police to deal with criminals.
Obviously there are numerous refutations, and that isn't lost on people. Many people will justify it by saying that regardless of the circumstances, the police put their lives on the line every day, so that gives them a pass when they make mistakes. Many people would view your suggestions as weakening the police, and the militarization of US police is viewed by many as making us safer, not less safe.