There are a few points that need to be clarified and some underlying assumptions perhaps rejected.

1. Marriage in Islam is allowed between any man and woman as long as they are not between the Quranically specified forbidden categories (mother (or any ancestor), daughter (or any descendent), sisters, aunts, etc). Cousins are not listed in this category. What is important to understand is that there is nothing within Islamic scripture that specifically encourages or praises cousin-marriage. Rather, there's nothing that forbids it. Similar to the Judeo-Christian tradition.
2. The reason behind cousin marriages is largely socio-economic. People who are poor struggle to hold on to their wealth, and as they have children, that wealth becomes further and further distributed. However, cousin marriage allows people to pass on wealth without it being split up as much, allowing that next generation to do a little bit better. If my grandfather has 20K that he split among his two sons, my father has 10K to pass on, and his brother (my uncle) has 10K. If they have children they'd be splitting their inheritnace among two children. Now imagine that I married my uncle's daughter. Both of those 10K amounts concentrate back into a single family, increasing our chance of surviving and thriving financially, and being able to move up in life or at least survive. This is the fundamental trade-off of first-degree consanguineous marriage - financial advantage for genetic disadvantage. Far from being a religious impetus, socioeconomics drove this force until it became a cultural staple in some (but not all) socities.
3. There are a number of narrations from Islamic scholars that discourage cousin marriage.

Hafidh Zain ad Din al Iraqi (d. 1404) was a major Shafi'i scholar and wrote that 'Umar ibn Al Khattab, the second Caliph, close friend and confidante and deputy of the Prophet Muhammad (s), discouraged people from marrying within the family. He said to a tribe that used to practice consanguineous marriages: "All of you have become frail and feeble, so marry outside of your families!!" (Al-Iraqi, in his Takhrij maa fil Ihyaa min al Akhbar of the narrations in Ghazali's Ihya).

The madhab of Imam Ahmed, the Hanbali school also mentions that people should marry outside their close clans or families because it leads to children being more fit and healthy.

Some more information is here: http://seekershub.org/ans-blog/2010/08/30/the-ruling-of-first-cousin-marriages-a-balanced-perspective/

So the idea that cousin-marriages can lead to weaker offspring was well known even at the time of the Prophet (s). However, the Shari'ah did not forbid it, and so this genetic disadvantage was sometimes taken in the face of even greater financial harm and difficulty faced by many families and cultures throughout history.

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The issue is not really for Islamic scholars to discuss as the issue isn't religious. The issue is for people in the medical and genetic sciences fields in many of these countries to advise people, write books, get on talk shows, and put out more information for the general public about the medical harms of this practice, especially when done for many generations. Religious law won't step in and force the marriage to become impermissible, but does allow for scientific and medical experts to educate and weigh in on the matter so people can make good decisions.