This question stems from a reading that suggest that one function of religions is to justify normative patterns of social order.
I think if you look at most religions from their standpoints on morality, money, committed relationships and acts of goodness, most would compare conservatively to the non-religious world. On the other hand, if people are not receiving direction on the above topics from a religious standpoint, are they receiving direction on them at all?
Keep in mind that there have been times in history where religons have been the radical force for social progress, as opposed to the conservative one inhibiting it. Archbishop Oscar Romero of El Salvador practiced Liberation Theology, the idea of the Catholic Church being the vehicle with which to achieve social justice. His practice of this idea was so radical it cost him his life - from violent conservative elements in his own country.
In the early 1800s United States, it was the religious women of the time who started such progressive movements as women's suffrage - very radical for the time - the Temperance Movement, reforming prisons into penitentiaries and establishing mental hospitals.
So I would say that often tiems religion is a conservative force, but there are enough exceptions throughout history to question the rule.
This is too big of a question to receive one reductive answer. At the same time, I think that any religions, and the notion of the question's assertion about "all" religions, are complex enough to have different branches or sects that might approach the notion of social progress differently. I can see how some aspects of religion do help to justify normative patterns of social order. The idea of being obedient and subservient to a higher power, to not overtly question and defy authority, and to make sure that productivity towards this higher end is something that is achieved can be easily moved from religion to state or social order. However, the notion of spirituality and individual discipline within this realm helps to create a divergent vision of social progress. Different individuals within different sects of faith have different beliefs on what social progress should be. Due to this, I think that the idea of religions being conservative or liberal will vary accordingly.
I do not think that all religions are necessarily conservative in all places. There will be times and places when the tenets of a religion will be "ahead" of the current social values.
I think it is probably true to say that all dominant religions are conservative. Any religion that really dominates a culture will necessarily be tied up with the values of that culture. In such cases, the religion will have to be conservative. You might see this, for example, in the Christianity of the antebellum South. This faith justified slavery and was therefore conservative.
But you can have religions that do not dominate a society and they can be "liberal." For example, you have religions in the US that are in favor of more gay rights than the general population wants. These religions can favor pushing for social change because they are not really tied up with the dominant culture.
Answer to this question depends very much on the meaning we attach to the word religion. If we think of religions only as a set of old and established beliefs and practices handed down to practitioners of each religion through centuries of tradition, and which are zealously protected by some section of people such as priests within the religion, then the religion is bound to be considered as conservative.
However, there is another view of religion. Most of the major religion were started off as reformist and progressive movements. By no stretch of imagination we can describe Jesus Christ or his immediate main disciples, as conservative. Most certainly, they were all reformist, and the ideas they promoted were most revolutionary. Even reformers of religions like Martin Luther were some of the most progressive persons in the history. Even the most illustrious believers in God and religion have been clearly very progressive and even revolutionary personalities. Three example of such persons, taken from different periods of history are, Saint Joan, Florence Nightingale, and Mother Teresa.
So, I will say that religion is not necessarily conservative. But like every other thing in the world, religions that are fresh and revolutionary at one time tend to get old, outdated and tradition bound over a period of time. Then people within the religion emerge from time to time, who recognise the limitations and aberrations of their religion, and take action to reform it.
It is interesting to note that Geeta, one of the greatest text of what is popularly called Hindu religion, explicitly recognises and accepts such reformation of religion, which take place from time to time. The exact words contained in verse 8 of chapter 4 of Geeta are:
Dharm sansthapanarthay sambhavami yuge yuge.
Lord Krishna, who is an incarnation of god says, "I assume physical form (sambhavami), from time to time (yuge yuge), to renovate (sansthapanarthaya) the dharm. Please note that the Sanskrit word dharm, which is loosely translated in English as religion, really means a code of conduct or rules of right behavior, rather than a set of religious rituals or practices.
I will conclude by saying that basic nature of all good religions is progressive. Conservatism is a defect that naturally creeps in them over a period. That does not alter the basic nature of religion. A knife can become blunt with use, but the basic nature of knife continues to be sharpness. Realizing this truth about the nature of religion will help us make the right and best use of religions as intended by their original leaders.