asks: How would I handle serious topics like, say, terrorism or atrocities like black slavery or the holocaust in a tasteful and sensitive way while still keeping a reader interested?

Such topics do need to be handled with tact and sensitivity. Some tips on how to do that...

Make sure the scenes you are portraying are accurate. Watch documentaries about the topic and read articles/interviews/biographies from survivors or historians. There's no need to exaggerate or be graphic in order to maintain reader interest. The plot and writing style is responsible for that. Just be truthful to the best of your ability.

Most writers are unlikely to do this, but it still needs to be said. Don't make the horrible things that happened seem like small, unimportant things. Don't make them seem like good events either. Saying things like, "Thank goodness the Holocaust happened, because ____." It doesn't matter what the second half of that sentence is. It will be offensive.

Yes, horrible things have happened, but that doesn't mean an entire race of people (or all the people of a country) can be blamed for it. Extremists never represent the whole, no matter how much they say they do. When we accuse all the people of a bad thing, we are fostering hate. Hate stirs up the wrong kinds of passions and we end up with senseless violence against the innocent. You may think, "But it's just a little story." You never know what kind of impressionable person is reading it. Each of us creates little ripples around us. Make yours positives ones, if you can.

offers an excellent tip:

I think it's important to say the hard things in your writing. The power of books is that they have the ability to turn thoughts and change minds because authors can be masterful at subtlety when it comes to approaching these topics. A few ways to do this and not be overtly offensive would be: make it a fantasy setting. Look at After Humanity which is a fabulous book on Wattpad which deals with slavery and puts a lot of thought into giving a realistic (though fantasized slightly for the world) view of it.

Make it for children: I think I was Dr. Seuss who said if the topic is too tough for adults, write it for kids. Take a second look at some of his work like the Butter Battle Book, The Lorax, and the Sneeches. These are extremely well done stories about prejudice, the holocaust, arms escalation, and destruction of the environment through material greed. The Harry Potter series is a fabulous look at what happens when people who believe only "their type" should have power (pure blood vs mixed blood). It's masterfully done and completely inoffensive.