For Lebanon its not that clear cut.
Not allowing the Palestinians work in over 70 different professions is wrong but the main reasons (for good or bad) are here:
1) Pressure on Israel (perceived) by making the plight of the Palestinians in the camps so miserable so as to advance the cause of the right of return.
2) Sectarianism (the main reason). The balance is already tipped towards the Muslim population. However, Sunni Muslims and Maronite Christians are the ruling class in Lebanon and their numbers are equal. The Shiites have strength outside the polical arena and this is changing for better or for worse. Palestinians are Sunni, to naturalize them would be to destroy the demographic balance and risk inflaming the fanatics within varioius Maronite movements.