It's not the customers fault that the ISP didn't design their network in such a way that someone using all the bandwidth that the ISP provides them causes problems.
Sure it is. It means they didn't select the service that meets their needs.
I think you misunderstand what I meant, I mean it's not the customers fualt that using all the bandwidth the ISP provides them causes problems for the ISP.
Sure if the customer has problems with their own connection when they fully saturate it that's their problem not the ISP's.
But it's certainly not the fault of the user that the ISP is giving them more bandwidth than the ISP can handle them using.