For starters you should not remove this content from your lessons. Secondly, your explanation to parents should be that these are real issues that we are facing in the world and it is important for our students to be aware of them to help them become democratic citizens to solve problems within their communities or country. It's great you have support from your principal because that would be a difficult battle to win if he asked you not to teach the materials. You should also ensure that your students have a very open and friendly forum of discussion about these topics. By allowing students to see that they can make an impact on these issues is incredibly important for a democratic society. Your example is something that I have not thought of using and will now begin to implement in my own classrooms. You could possibly allow your students to research their own statistics on what interests them and let them create their own solutions to the problems they find using math!