In spite of what its critics say, the new, expensive artificial kidney

Responding to a pm:

Analogy means "similarity".

Now focus on the argument:
The new, expensive artificial kidney implant is a boon to modern medicine.
Critics should remember that the first heart transplants stimulated an enormous amount of beneficial medical research, even though the transplant technique was later rejected in favor of less invasive surgical procedures

So the author is implying that first heart transplants were very beneficial because they stimulated research. Similarly, artificial kidney implant is a boon too. The implication is that it will stimulate lots of research too. So the procedure itself may be difficult and expensive but it will lead to research on more useful procedures.

B. implying an analogy between the benefits of the artificial kidney implant and the benefits of the early heart transplants
So the author is defending the procedure by implying similarity between the early heart transplants and artificial kidney implant. This is correct.

E. implying an analogy between the critics' opposition to the artificial kidney implant and their opposition to the early heart transplants
The author does not say that these same critics were opposing early heart transplants. Had the argument said that, then it would have implied an analogy (similarity) between the critics' opposition.

Circular reasoning is a logical fallacy (false logic). You begin with what you are trying to prove. Circular argument uses its own conclusion as one of its premises.

e.g.

He told me that he doesn't lie.
He always speaks the truth.
Hence, he speaks the truth.