wa alaikum as salam
I dont need to look into the matter. unlike imam sahab I have worked in financial services with the largest banks in the world as employee and as a consultant, and understand the operations ranging from institutional asset services to syndicated securities to lockbox services to retail banking. I am not standing up against the person, but using his own logic, I can understand if he says that working in a bank dealing directly with interest is not allowed (even though my personal views consider interest and riba different) but a security guard at a bank is not dealing with interest so is there an issue with his earnings being not allowed because the source of income for the bank, from which he is paid are interest based?
if dealing with interest is not allowed …and the govt has a lot of loans on which it is paying interest, and those loans are then used to pay for govt programs and salaries, they are impacted by intrest as well. the govt is reciever of interest as well as payer of interest. govt insitutions like universities and colleges are thus impacted by interest and salaries of these people are haram by your own example.
That is your opinion and has nothing to do with facts. are you saying that in western countries all the donations that groups like red cross or cancer research or march of dimes or humana etc get are from people who dont take interest?
or did you mean non western charities? because muslim interest takers are different than non muslim ones? 
do you also mean to say that all the pakistani and muslim charities who get funded by overseas pakistanis get their funding from people who have non interest bearing accounts or investments that have nothing to do with interest?
even if one person who takes or gives intrest donates some money to the masjid and that goes to pay imama sahab’s salary, does it make his job haram, please ask him that and see him back peddle out of it. I have seen this before, heard this before and made the exact same argument and then heard aaen baaen shaaen in response.
you may continue to disagree.