If the one who carried out this attack turns out to be like so many before: 'small time criminal, radicalised in prison, known to the authorities' there is a limit to the number of times you can argue they need to be free to keep tabs on the real terrorists. This was one of the deadliest attacks ever, it does not get more real then this.
Those who are "remotely suspected to being extremist" have not the same profile of the terrorists themselves. If they go the same mosque, are related or have some friends in common that enough.
Again, if you really care about safety, deporting everybody who can be "remotely suspect" is the worst way to deal with terrorism, since they are the visible tip who can lead to the real danger. Real terrorist are smarts. They don't show any sign of outside radicalism. The process is usually like this: slow radicalization that show -> quick escalation that lead to the internal adoption of terrorism and the external rejection of all signs that could point toward this. The "posers" are in general not an immediate danger. They are very useful because they can lead to the real danger.
Again, when we say "remotely suspected", we don't even speak about them. We speak about any kind of muslims. In France, after november 13, a lot of people (+10 000) were found to be " suspected of extremism" and where the one watched by anti-terrorism police. Some of them turned out to not even being muslim in the first place, others where ultra-conservative preachers which were on ISIS hit list.
This brought to light that the REAL terrorists were not in that list and it was the broadening of the definition of "extremism" that facilitate the works of the terrorist. If you're gonna put everybody who get off jail with a big beard, you'll end with 99.99 % of people who don't have anything to do with terrorism. People don't realize that we're speaking about hundreds of potential terrorists in midst of millions of "visible" muslims. And they are often less "visible" than the average muslim.
The uncomfortable truth is that we will never be able to fully defeat terrorism. You have to maintain a balance between security and liberty, because we will never achieve full security. Our antiterrorist services is stopping dozen of attacks each years and it's pretty amazing. We don't need some populist call who would make their jobs harder.
As much as such words are needed when an attack happens such as "we won't let terrorism defeat us" and "unity everyone", try being the parent/family of a child killed. 
