Mastectomies are back in vogue: Blame it on celebrities such as E! talk show host Giuliana Rancic and comedian Wanda Sykes, who appeared to bounce back easily after their recent double mastectomies and reconstruction for early-stage breast cancer in one breast. Or blame it on the overwhelming need to have some peace of mind after receiving a frightening breast cancer diagnosis.
Regardless of the reason, surgeons have seen a surge in requests from breast cancer patients who opt to have both breasts removed (including the one that’s cancer-free) rather than removing just the malignant lump in one. That’s despite findings from seven large clinical trials, which showed that, for tumors that hadn’t spread beyond the breast, mastectomies didn’t provide additional benefits over more conservative surgery — called a lumpectomy — followed by radiation.

Comments
There are a number of other reasons not mentioned in the article:
1. My understanding is that the lifetime possibility of cancer in the other ('healthy') breast is 20%; in half of these cases the cancer is metastic - meaning it will kill you. Especially with good reconstructive options, and if you have completed your family and breastfeeding is not an issue, most people would not want to go through life with a 10% possibility that a breast may kill them.
2. Chemotherapy is, for many people, much more debilitating than surgery. It took weeks (not 3-6 months) to recover from a (single) mastectomy and literally years to recover from chemo. The possibility of needing chemo again, when it could be avoided, was for me untenable.
3. Cosmetically, a well-reconstructed breast looks different, and often much better, than a 'natural' breast; sometimes size is different as well, which is a challenge in choosing and wearing bras and clothing. A breast lift may help 'match' the two, but this is just as invasive as mastectomy.
I'm sure there are other reasons as well which vary from woman to woman. There may be realistic fear involved, but these choices are a long way from 'irrational fear'.