Hizb ut-Tahrir describes itself in its manifesto as an "ideological group". Its declared goal is to establish an Islamist State: a modern Caliphate with an elaborate constitution and canons.
Within that framework, the Caliph is head of state, who legislates all laws, and decides on each article of the constitution. The Caliph also appoints and removes the judges, the heads of the army, and governors. Hizb ut-Tahrir also explains that all parties which are not "Islamic" – in their view – would be banned. By this they mean any democratic party, human rights group or in fact any group that doesn't believe in its archaic and pre-modern version of the Sharia, which includes killing apostates. It also explains that military Jihad is a duty and every 15 year old is obligated to prepare and train for Jihad. It seeks to create this imperial State in Muslim majority countries, but not in the west. In the West its goal is to generate an acceptance if the ideology as an alternative to Capitalism or Socialism for the entire globe.
It has been argued therefore that the organisation’s ideology is not dissimilar to ISIS. It believes in an expansionist State; it doesn't recognise borders between Muslim majority countries; it would execute homosexuals, adulterers and as stated apostates including those Muslims that believe in democracy.
After the recent attacks in Denmark and incidents in Australia there have been calls to ban the group. Part of the UK government counter-extremism strategy is either to ban the group for being anti-democratic or ban them from having public events. Hizb ut-Tahrir responds that is has previously condemned various terrorist attacks including those of 9/11 (on grounds that the planes were not state owned but privately owned!). However it does believe that militant Jihad to take over countries does not require a Caliph and that in such a Jihad, killing even elderly men if they pose a potential harm to the Muslims is acceptable; that hijacking Israeli planes was acceptable and that killing all Jews in Israel, if they refused to abandon the Israeli territory, would be necessary. However despite being repressed, having had its members tortured, and suffering many members killed brutally by various regimes (the most latest being ISIS) it has resisted resorting to violence and organising terrorist acts itself. It did however take a pledge of support to its leader in Syria from various jihadist brigades to establish their Caliphate in Syria aimed at overthrowing the "unbeliever" Assad.
Hizb ut-Tahrir's methodology is to seek material support from armies and influential factions in society with the goal of overthrowing regimes in Muslim majority countries, primarily by coup and then through military force bringing down all other states and unifying those countries into a super-state. Whilst the ideal is a utopia, like all utopian visions it arguably has been influential in creating the Frankenstein versions such as seen in ISIS.
As it does not violate any of the specific laws in the UK, or Denmark, it has not been banned, despite two previous attempts to do so. Individual members though have been convicted of offences related to inciting violence for distributing leaflets calling for killing Jews among other things. Recent Anti-Semitic speeches have also caught the attention of the Australian authorities. Omer el-Hussain, the shooter in the February attacks in Copenhagen, attended a Friday sermon delivered by a member of Hizb ut-Tahrir the day before his murderous spree.
Whilst it is correct to observe that Hizb ut Tahrir is not a terrorist group, and they have not undertaken acts of violence or call for terrorism, it does believe terror is legitimate. Accordingly, it has been argued that they are a source of extremist ideology and a radicalising force. Whilst it is not accurate to describe Hizb ut-Tahrir – as some have – as a conveyor belt to terrorism, it is equally wrong to see it as some kind of vent for Muslim anger. It actually perform the opposite role. Hizb ut-Tahrir incites anger, justifies terrorism, and has created many offshoots which have become terrorist groups. These have acted on Hizb ut-Tahrir's most extreme religious and ideological positions. As part of its methodology, Hizb ut-Tahrir seek to generate anger and direct it against governments, and seeks to prevent integration of Muslims into western societies, rather than merely venting anger as some have claimed. That is why it is necessary to expose its ideology and critique its politics, and its ahistoric narrative of a glorious single Caliphate which existed from the time of Muhammad until the end of the Ottoman Empire. We must demonstrate clearly that their narrow anti-democratic religious interpretations are far from being mainstream. To ban them would be both illiberal and a failure to win the intellectual argument against extreme Islamism. If we can't defend our ideas and values from fascists of a religious bent, then we have truly adopted our values - as Mill feared - as merely dogma and have failed to understand, apply and uphold them.