That's my whole point, far from protecting AGAINST terrorism you just fuel new recruits TO terrorism. I cannot imagine that it's very much different in for example Bradford today where someone sees someone they know dragged out of their house at dawn and locked up without trial, than it was in Belfast when I was a lad. The sheer seething hatred and resentment felt by the communities I think is seriously underestimated by co called intelligence officers, and aside from it not being morally right to inter people without trial, it simply makes a bad situation very much worse. The reason terrorists are so successful is that they are ordinary people turned to terrorism by either what they have seen, heard, witnessed or otherwise absorbed from people in whose interest it is to radicalise them.That's why it's relatively simple for them to go undetected. You really don't want an army of normal people trying to sabotage your infrastructure because you've locked up a few loud mouths you don't fancy the look of.
Now if you suspect soemone of being up to no good, no right minded person would be against you bringing them in, holding them and quesitoning them for a sensible amount of time and either charging or releasing them and I myself amd quite happy with 7 days, but 42 days is far and away too much and gives the govt way too much leeway to abuse the system.