I'm sure I could write a piece on the idea of 'enough is enough' and the 'instant society'.
We don't have much patience in politics nor in long term political thinking in the UK in 2017.
The UK and US are world leaders in the 'instant society'. Where things happen just like that, and things are black and white and can be solved by amazingly simple solutions.
If only.
As for extremism, violence behaviour is already illegal, last time I checked. They are designated as terrorist groups. Indeed many Islamic extremist groups are already proscribed for promoting violence.
[https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/612076/20170503_Proscription.pdf]]
This comes under the Terrorism Act 2000.
Section 1. –
^(1) In this Act "terrorism" means the use or threat of action where-
(a) the action falls within subsection (2),^
(b) the use or threat is designed to influence the government [or an international governmental organisation][2] or to intimidate the public or a section of the public, and
(c) the use or threat is made for the purpose of advancing a political, religious[, racial][3] or ideological cause.
(2) Action falls within this subsection if it-
(a) involves serious violence against a person,
(b) involves serious damage to property,
(c) endangers a person's life, other than that of the person committing the action,
(d) creates a serious risk to the health or safety of the public or a section of the public, or
(e) is designed seriously to interfere with or seriously to disrupt an electronic system.
(3) The use or threat of action falling within subsection (2) which involves the use of firearms or explosives is terrorism whether or not subsection (1)(b) is satisfied.