Do you think they'd except an essay that talks about why there are obstacles for people (only because they allow them to be) and expand on that idea?
It depends on how you go about it. In one sense, what you have said is quite correct. Most of the people I know face primarily problems of their own making. In fact, they grapple their personal pain to them, clinging to it as if they had mistaken it for a life-preserver. If they simply chose to be free of their problems, they really would be. Recognizing this shows great wisdom, and is commendable.
On the other hand, it could, as others have said, be taken in another sense, as being arrogance and folly. For instance, children who get cancer might reasonably not view the cancer as an obstacle they suffer from only because they allow themselves to be sick. People born to drug-addicted prostitutes or to abusive parents, or to wonderful parents living in a war-zone, all might legitimately view these obstacles as ones that were entirely beyond their control.
The other comments you have received have clearly interpreted what you have said more in the second sense. This could just be because you provide so little to go on, but it points to a potential problem. If you go with this, then you must be sure to explain that you are talking about a particular subset of problems, and that you do not mean to belittle the genuine hardships that people may encounter through no fault of their own.