I will try to provide you more details.
(1) Too much of them and hard to maintain:
If we need to create one graph for every triple or every resource, we would end up with billions of graphs. That is already hard to maintain.
Also, there is no way we include that much FROM clauses in our select statements. And those statements would be hard to maintain too.
(2) Would probably not be enough:
If we take the example of the organization and put each of them, with their triples, in a different graph. That is still not addressing the need to restrict the view of the organizations associated with portfolios assigned to each users. We need to go one step further and restrict based on portfolios.
Also, as each organization can be associated to many portofolios, we cannot create graphs for portfolios and include the required organzations there.
Finally, the portfolio example is only one example. There could be other ways to restrict organizations. And the graph segragation used for portfolios, would not address the other requirement.
I am not sure exactly what you are referring to. If you can point me in the right direction, I will have a look.
(4) Overall, you might be right and maybe there is something I am not getting about what Stardog can do for fine grain security. But if this is true, please just provide more documentation.