Europe doesn't clearly have a security problem. A few insane people committing political violence doesn't change the fact that Europe is among the safest places on the planet.
Even if it's not a problem today (in your opinion), then either that trend has to be reversed or it will become a problem at some point.
In 1972, there were over 12,000 shooting and bombing attacks in Northern Ireland; by 1977, this was down to 2,800.[41] In 1976, there were 297 deaths in Northern Ireland; in the next three years the figures were 112, 81, and 113.
Just because some number has increased, that doesn't say anything about whether it will increase further, and if so, at which rate. So: How do you know there is a trend in the first place?
But seriously, no one is saying they don't want to "reverse" things. There are just many ways to do that that actually solve the issue (old fashioned going out and getting the bad guys?) that don't diminish our rights.
[0]: https://twitter.com/BaltimorePolice/status/75552242792132608...
See http://www.economist.com/blogs/graphicdetail/2015/11/daily-c...
Last year, that increased to around 100, this time based on 2 attacks (both in Paris, France).
So far this year, there have been nearly 300 fatalities over 9 separate incidents: http://www.latimes.com/world/europe/la-fg-europe-terror-2016...
Correction: there were around 170 fatalities in 2015, and there have been around 150 so far in 2016.
I have a couple of ideas why this may be so:
a) Back in the seventies/eighties when media reported on the Troubles in Northern Ireland, the ETA in Spain or the RAF in Germany / BR in Italy, reporting was much more low key (For anything but the most spectacular events, Norwegian papers would typically publish a small note to the effect that "Members of the Basque separatist organization ETA today killed a police officer and two bystanders in whatever Spanish place you've never heard of."
Today if someone for whatever reason kills a couple of people, it is a major story with photos, interviews, analysis and whatnot. Hence, events on a similar scale as was experienced in the past now appear much more significant.
b) Violence today seems a lot more arbitrary; in the seventies, the typical terrorism victim if my recollection of the news back then is anything to go by, was someone who was targeted for something they were; police officers, magistrates, cabinet members, Israelis, whatever.
Hence we'd just shrug it off, as we weren't targets, anyway.
Today, for a significant number of perpetrators, anyone is a target - and that makes it a lot harder to just shrug an attack off as something which does not affect you; three people get blown up in a bar in Elbonia? Could've been you; after all you went to the neighbourhood pub only yesterday!
c) Additionally, as much (if not all) terrorism today appears motivated by religion (or, more precisely, by some perverted interpretation of religion), it is a godsend to anyone of a xenophobic bent. Get rid of the people you do not like; get rid of the terrorism problem at the same time!
Militant islamism basically makes xenophobia legitimate, which in turn can be argued to foster militantism, which further fosters xenophobia and downwards we go.