I am a PhD candidate and I have been offered an internship that I want to take. My advisor objects. Should I take it anyway?
Make a decision. Do you want a PhD or not. If you do, then make that the priority. Such opportunities as the internship will probably come along later. The doctorate would probably be harder to restart if you stumble.
Your advisor is giving good advice provided that the PhD is what you want.
Slowing down your research may get you scooped before you complete it, requiring at least a partial restart. Why take a chance.