Is it permissible to deal in the shares of companies that deal with usurious banks if these companies are essential to the lives of Muslims, and if Muslims not participating in them leads to non-Muslims dominating them? And does the principle "warding off harm takes precedence over acquiring benefits" apply to this situation?

The ruling on buying and selling shares of companies varies depending on the nature of their work:

1. Companies with permissible work: It is permissible to buy and sell their shares, unless they deal in usury (riba) or offer prohibited services.

2. Companies with prohibited work: It is not permissible to buy and sell their shares.

3. Companies with permissible work but engage in prohibited practices (like dealing in usury): It is not permissible to buy their shares, because the means to a permissible objective must be permissible, and the end does not justify the means.