While this type of incident does happen it is hardly on a "...regular basis in small towns and large cities in the USA." I base my opinion on 27 years in law enforcement.
As far as visiting places like Paris, consideration should be given to the US State Dept's travel alerts.
"Recent, widely-reported incidents in France, Russia, Sweden, and the United Kingdom demonstrate that the Islamic State of Iraq and ash-Sham (ISIS or Da’esh), al-Qa’ida, and their affiliates have the ability to plan and execute terrorist attacks in Europe.
Extremists continue to focus on tourist locations, transportation hubs, markets/shopping malls, and local government facilities as viable targets. In addition, hotels, clubs, restaurants, places of worship, parks, high-profile events, educational institutions, airports, and other soft targets remain priority locations for possible attacks. U.S. citizens should exercise additional vigilance in these and similar locations, in particular during the upcoming summer travel season when large crowds may be common."
This is the link to the full alert.
https://travel.state.gov/content/passports/en/alertswarnings/Europe.html
I fought in two separate wars in my life and I'm done with the "it'll never happen to me" syndrome. if you push the envelope long enough it darn sure will happen to you.