It's neither good nor bad. It's just a thematic choice.
If you write it very effectively, yeah it's good. If you don't know how to do it in a striking and fun way there's no point in doing it.
I mean, why write difficult subject matter if you're not going to tackle it with good research and a strong emotional understanding? Why write a violence-heavy comic if the violence is going to be all same-y and unoriginal?
Write things with dark themes if you want but you MUST do the necessary research to approach it well. You MUST make sure you're doing it with a lot of heart and soul.
An example of dark themes done badly? Blue Velvet, Fifty Shades Of Grey.... there are plenty to choose from. They come across as tone deaf and aren't written or directed in a way that really makes any of the dark occurrences feel acknowledged, or memorable. I can't even count the number of times Fifty Shades has included straight-up rape or abuse and just mistaken it for romance. I can't count the number of times Blue Velvet made me feel either insulted or just plain bored. Both try to tackle "dark" ideas but do it really poorly and without much thought.
On the other hand, dark themes are handled in Hannibal (the red dragon) absolutely perfectly. They're done in a way that's memorable and actually sympathetic. They're handled with the right amount of care, and the emotional beats are almost never missed. Same thing goes with Silence Of The Lambs. Other examples I know of include things like Until Dawn, Ghost World, Frankenstein... I could go on for a long time about how these works take darker or more taboo themes and make really beautiful, poignant stories about them.
As long as you're ready to handle the themes and the weight they carry, go ahead. Just don't tackle it until you're ready... I've seen a lot of young writers try to tackle very heavy stuff early on without sufficient perspective, and the results are often pretty disastrous. It's not a good idea to take on something you're not ready for. Planning and research are super important, ESPECIALLY for dark themes.