The internet is a great tool for research however it also does provide an avenue for everyone to post comment, regardless of agenda or belief.
The only thing that we can use as the correct answer is the actual statistics in regards to side effects noted. We have prescribed around 17,000,000 Finasteride tablets since inception in 1996. To date we have not had one long term side effect noted. Finasteride is a fantastic medication if it is prescribed correctly and the patient understands the full profile of the medication.
Here is a very balanced piece on Finasteride.
http://www.the-dermatologist.com/content/does-finasteride-lead-permanent-sexual-side-effects
Our biggest problem is allergic reaction with the topicals. We have eight different versions due to skin issues. This happens in around 1% of cases however due to our high numbers of patients we have to deal with this on a daily basis.
The 2% failure rate is not really due to the patient having a side effect, it is simply that the program is not getting us more hair back.