Saying crispr is controversial is like saying dynamite is controversial. It's a tool that will change the world in many amazing ways, it is not in and of itself good or bad. The application of crispr has already improved the world and the lives of people in it. But as with any powerful tool, it could be used in an unethical way in the future.

https://youtu.be/jAhjPd4uNFY

If you haven't watched this video, I recommend it. (Fixed link)

If you prefer to read, this article might be more your speed.

https://www.economist.com/leaders/2018/11/08/gene-drives-promise-great-gains-and-great-dangers

A DNA editing machine! Excited by the possibilities! Concerned about people who'll use it to hurt others. This type of progress is a good thing, overall. It feels like they've just discovered a steam engine but we haven't even approached the possibilities yet.

CRISPR is more discovery than invention as it’s the cell’s existing system for fixing errors in your DNA. So you already have it.

I’m sure vaccines may have been controversial for some initially too even though like CRISPR, they use the body’s immune system. A traditional dead virus vaccine makes your body think you have the virus so it prepares to fight it. When the real live virus comes along, the immune system is prepared.

So we now are starting to use CRISPR to fix/change other things. This one (brain cancer) is a great example. Could it be used for evil? Sure so could many things we use every day. A car can be used to quickly get you from home to work but it can also be used a weapon.

Science tools are amoral. Science applications may be controversial / immoral. CRISPR is the former. That's all.