Islam still has to follow the law of the country

It is mentioned in the Constitution of Pakistan that no law could be formulated that violates the spirit of the Holy Quran or the sayings of the Holy Prophet (PBUH). Now I do not mean that following the life of the Holy Prophet (PBUH) is to enforce all such laws of his time that were in line with the socio-cultural norms of that society and which he himself followed to some extent without much alterations made to it. For instance, slavery was prevalent during the time of the Holy Prophet (PBUH) and even though he advised men to keep good attitude to their slaves and mentioned it was better to free them but did not at once asked them to put an end to slavery or ordered punishment in case anyone kept a slave. However, the Holy Prophet (PBUH) set the environment needed to change the old tribal traditions.

The Prophet (PBUH) himself married his close relative to a slave and declared free the child mothered by a slave woman. Due to the prevalent cultural, economic, and war conditions, no drastic changes were made but gradually the tradition of slavery had faded to the extent that no Muslim country allows it in the present times. No such law can be seen practised even in Saudi Arabia where pure Islamic laws prevail. Now it will look absurd if we allow slavery to prevail once again. During the time of the Holy Prophet (PBUH) only the prisoners of wars could be kept as slaves. Should we follow the same law and deviate from the Geneva Conventions? Would it have been just to us had India made our prisoners their slaves in the 1971 war on the pretext that it was allowed in our religion?

If such laws were not demolished by the Holy Prophet (PBUH) during his life, it does not mean they were all Islamic. We need to understand the spirit of Islam and make laws accordingly for the present times. Islam clearly states that the consent of both the subjects is necessary for a marriage to take place while they should also be above the puberty age since only a mature boy or girl could take a rational decision regarding his or her marriage. Even though immature marriages took place during the times of the Holy Prophet (PBUH) but that does not provide a license for its practice to this day.

I meant to post this to able 1 in a PM, but hope you will find it here anyway.