Among Jews there are two classes of `avadim, `avdei Yisra'el (Jewish slaves) and `avdei Kena`an (non-Jewish slaves). There are special laws pertaining to each one.
While I do not think slavery is itself a positive mitzvah, there are cases when a thief or debtor cannot make restitution and he is sold by the Beit Din for that purpose.
According to Rabbi Yirmiyahu Bindman, the sovereign power of a nation has the right to abolish slavery, which is what ours did in 1865. Plus, the slavery that existed in America prior to that time was not, as I understand it, in conformity with halakhah.
Whatever the case, the fact is that the Torah is Perfect and Eternal, and when Mashiach comes he will restore it in its entirety. This means that all those "irrational" laws and regulations which are repugnant to the modern mind will be reinstituted.
I doubt very seriously if the slavery practiced by moslems is halakhic, but I would be very careful about attacking something sanctioned by the Torah because it doesn't fit our modern, secular mentality (I also wince when conservatives attack islam for being "theocratic").
Besides, slavery still exists in this country. It's called "working for somebody else," and the massa doesn't even have to take care of you. Of course, you have the right to quit your job, but the right to starve comes right along with it.
There is a saying that, One who aquires a slave for himself also aquires a master.
This also includes the knowledge that in Jubilee years that all slaves were set free. That would be every 50 years. If one aquired a slave the year prior to a Jubilee year, he would have to release that slave the next year. In addition, the master is responsible for the total well being of the slave and would be held accountable for it under the law.
The laws of Jewish slavery are not simple and have consequences for both slave and master.