Afaik, this goes for USA, Britain, Israel, Germany, Spain and Italy. And probably more cases. (Note "continuing problems". e.g. Breivik was a lone crazy.)
The reason is shown by the grandparent comment; terrorism is optimized to scare voters. And politicians are scared of hysterical voters, they need to fix that to keep their jobs.
Most every government (whether or not it is a democracy, and whether or not it actually has serious and continuing problems with terrorism) latches on to terrorism as an excuse (though rarely the only excuse) to throw off legal (and/or traditional, depending on the nature of the--note the small "c"--constitution) constraints on the powers and activities of government.
> The reason is that terrorism is optimized to scare voters.
True.
> And politicians are scared of hysterical voters, they need to fix that.
Less true; politicians have a often want hysterical voters -- hysterical voters that can have a prepackaged solution (even if the conception has little to do with the problem that has made the voters hysterical) are very popular with politicians, because its how they get approval to do things that they want to do that would, aside from the hysteria, never be acceptable. Note how many of the measures adopted in the US in response to terrorism were things which had either been tried previously under other pretexts (most recently, in many cases, in the Drug War) -- either proposed as legislation and failed, attempted without legislation but ruled illegal without supporting legislation, or had legislation passed but ruled unconstitutional when adopted for domestic law enforcement purposes.
And no, if there is a terrorism problem scaring voters the politicians are empirically motivated to fix it -- see my examples of throwing out the law book -- or it isn't a democracy. [Edit: To be clear, I think the Drug War etc are different; propaganda -- not really about scared voters.]
Afaik, despite this the courts in Israel seems to better keep up rule of law than the US ones, re terrorism... Which is sad.
But I think that without terror problems, the situation would be very different in Israel. And you probably agree.
Edit: I think you missed my point a little. I didn't discuss if it is right to throw out freedoms or not, I noted that empirically democracies seems to be very likely to do that in a certain situation.