It's not an antonym, people train all the time so their response times are quicker, but don't try and obfuscate the point- response times by police, however well trained they may be, allow way too much time for really bad things to happen. Only people who are prepared to deal with the issue on the scene are in a position to make much difference.
My guess is "assault rifles" aren't the culprit in most of those. How do we fix the social issues that lead to these shootings? You are never going to get a total ban like Japan. The bad guys will always be up to no good. What are the good guys to do?