Is the charging of low interest by AKFED and other Ismaili banks against the fundamentals of Islam?
Firstly, nowhere in the Qur'an is interest banned. However, usury is banned. The Qur'an defines ribat not as interest, but as usury — the only examples the Qur'an gives about usury are doubling and tripling of the principal amount. Usury is charging unreasonably high interest so as to basically scam the borrower.
O you who have believed, do not consume usury, doubled and multiplied, but fear Allah that you may be successful.
– Qur'an 3:130
Usury is condemned, but free and honest trade and agriculture — in all its forms — are encouraged, since they manifest a Divine service, and the welfare of mankind depends upon the continuation and the intensification of these legitimate labours.
– Imam Sultan Muhammad Shah, Chapter 2: Islam, The Religion of My Ancestors (The Memoirs of Aga Khan III), 1954
The idea that ribat refers to modern interest is nothing more than Muslim jurists using qiyas (analogical reasoning) to apply something from seventh century Arabian conditions — where there was no modern banking system — to the modern day environment, and it is really nothing but speculative guess work. In fact, Many Sunnis in Western nations are allowed to participate in interest transactions like buying a house, having bank accounts, and stocks and bonds out of the principle of "necessity".
Ismailis shouldn't worry about what Sunni jurists are saying because Ismailis don't follow a Sunni method. It is the Imam in each age, being divinely inspired and holding divine authority, who knows best what interest is okay and what is forbidden.
Even if the Qur'an forbade something and even if it did ban interest, the Imam can reverse it and make it permissible. The Qur'an was guidance given for the space-time and responsive to the situation. That is the meaning of Kitab — divine guidance that is speaking to the people in their own situation, background, and conditions.
The Qur’an’s kitab is not a book in the generally accepted sense of a closed corpus. Rather, it is the symbol of a process of continuing divine engagement with human beings – an engagement that is rich and varied, yet so direct and specific in its address that it could never be comprehended in a fixed canon nor confined between two covers…The logic of the Qurʾān’s own approach demonstrates the impossibility of understanding al-kitāb as a fixed text, a book.
– Daniel A. Madigan, ( The Qur’an’s Self-Image, 165)
When the Prophet said that the Kitab always remains with the Ahl Al-Bayt, it does not mean that Muslims are bound by the Text of the Quran (which the Prophet never compiled and which didn't exist then). Rather it means that the Imāms always possess and provide the Kitab (divine guidance for every situation that arises in that time and space).
"If Islam is ever to fulfill its mission it must have universality not only in space, namely, throughout the earth, but in time, namely, as long as mankind exists on this globe… we are entitled to adjust the forms to the facts of life as circumstances changed. It is the same Prophet who advises his followers ever to remain Ibnu’l-Waqt (i.e. children of the time and period in which they were on earth), and it must be the natural ambition of every Muslim to practice and represent his Faith according to the standard of the Waqt or space-time.”
– Imām Sulṭān Muḥammad Shāh Āgā Khān III, (Foreword to Muhammad: A Mercy To all the Nations by Al-Hajji Qassim Jairazbhoy)