The main argument is from Rom 7:1-3 (NIV)
1 Do you not know, brothers --for I am speaking to men who know the law --that the law has authority over a man only as long as he lives? 2 For example, by law a married woman is bound to her husband as long as he is alive, but if her husband dies, she is released from the law of marriage. 3 So then, if she marries another man while her husband is still alive, she is called an adulteress. But if her husband dies, she is released from that law and is not an adulteress, even though she marries another man.
First Paul is taking something that would be familiar to his readers, something they may have understood, and saying that our first husband (calling all Christians women!) was sin, but now we have died to sin, (or perhaps sin has died) and we are now free to marry Christ.
Paul does this elsewhere, citing an understanding or practice without questioning the practice itself. 1 Cor 15 Paul talks about being baptized for the dead.(verse 29 and following). He does not say whether this is a good practice or not (the idea was adopted into Catholicism), rather his point is that without a resurrection then there is no point in the practice because the dead will not then be raised. So there must be a resurrection.
Paul will use illustrations to make a point, and he is not there teaching on that practice, but rather using what people think or do to make a point. This passage only reflects the understanding of marriage that was previlant (sp?) at the time, not even what the Christian understanding should be. It is passages like this that are used out of their context that make Paul seem to people to be anti-women, and oppressive.