There is a common misconception that if you write fantasy, nothing or not everything has to make sense. In essence, the idea is that you can write whatever you want and get away with it because "There are no rules." 

That's an incorrect statement. Fantasy does not mean there are no rules. It means there are different rules. The rules of the real world can be removed, altered, replaced, or supplemented. In that sense, yes, you can write whatever you want.

However, once you've instituted these new rules, you as a writer have the responsibility to adhere to them. Anything that you write that does not follow the rules of normal reality must be explicitly explained or at least easily inferrable from existing explanations, and then anything that doesn't follow your invented ones will be seen as a logical error on your part. If you write something inconsistent with the conditions that you have set up for your story, then that means you were either careless or didn't fully and deeply explore the implications of your system.

The more you change the rules of reality, the more you will be forced to think outside of your habitual and instinctive perspectives. Also, a single change can have many and/or large-scale implications, so you have to be careful. For example, most people do not understand what true "weightlessness" is. Literally removing the gravitational force would dramatically alter the entire universe, and any astrophysicist will be quick to tell you what the implications of that would be.

If anything, writing fantasy means you have to be more vigilant about your writing, otherwise you might run into a convoluted mess of contradictory and illogical situations.