I have been told that it is Fard for me to be part of a Islamic group working for Khilafah due to the fact that the whole of the Sharia cannot be implemented without the ruling system, please help, the particular group that I am talking about is Hizb ul-tahrir, they say that they are the only group that work with Rasoolullah's (salal lahu alyhi wa salam) methodology.

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
Hizb at-Tahreer is a political Islamic party, calling towards Islam and towards establishing the Islamic government (al-Khilafah). This is the main aim of this party. This group has many independent opinions, which are criticized by the majority of the Muslim Scholars. Al-Sheikh Taqeuaddin al-Nabhani is among the well-known persons of this party. He is the founder of this group. He was born in 1908 AD and died in 1977 AD. He is from Palestine. After completing his pre-degree study in his village, he joined the Azhar University. After his graduation he became a teacher then a Qadhi (Islamic judge) in various villages of Palestine.
After the disaster of 1948 he left his country and migrated to Beirut. After the war he became a member of the Islamic court of appeals in Jerusalem then a lecturer in the Islamic College of Amman. In 1959 AD he founded his party and devoted himself to its leadership, and wrote many books and booklets which are the source of this group's opinions. He died in Beirut.
Creed or goal of this party:
I. The main abjective of this party is to turn again towards Islam through establishing an Islamic government in the Arabic States first of all then in other countries.
2. This group spends much effort educating people till they become a good example of Muslims.
3. They try to strengthen the faith in Islam through spreading the Islamic awareness as well as working in the political field.
4. This party neglects the spiritual matters and view them from a philosophical point of       view.
There are many drawbacks for this party; some of them are as below:
1. In the matters of Dawa'h.
A: Concentration on the ideological and political fields neglecting the spiritual matters and the matters of training according to Islam.
B: Being busy debating with other Islamic organizations.
C: Giving much importance to logic in the matters of creed and in building an Islamic personality.
D: Giving up the job of enjoining virtues and forbidding evils.
E: The main purpose of the members of this party is to take over the government.
II. In the matters of Fiqh.
This party adopted many strange ideas, that do not have any relation to the Islamic Sharia; some of them are as below:
1. A non-Muslim or a woman could be the member of advisory board in Islamic government.
2. Seeing the naked pictures is permissible.
3. Kissing an alien woman is permissible. It does not matter whether it is for sexual desire or not.
4. It is permissible to have a Kafir ruler of a Muslim State. And there are many views, which are contradictory to the clear teachings of Islam.
Allah knows best.