There is no evidence to suggest that propecia is at all dangerous. Sometimes the doctor will recommend a liver function test before starting because it could potentially be toxic to the liver, but my understanding is that is rare and therefore is almost never cause for not prescribing it. Likewise, minoxidil (or rogaine) is not at all dangerous so long as it is applied topically and not ingested (it's original purpose was as a vasodilator to control blood pressure---they noticed people regrowing hair who took it). If you want to check, the complete list of propecia's problems are listed on rxlist.com
A word of warning: propecia (finasteride) is a five-alpha reductase inhibitor, and blocks the dihydrotestosterone breakdown which causes the hair loss. Therefore it works on the anabolic pathway, and to pregnant mothers it presents a significant risk. Were a mother to ingest it, the fetus could develop abnormal external genitalia (bad). Therefore, women are warned to stay away from this drug, not to even touch it.
Because of it's potential action on the anabolic pathway, bodybuilders have theorized that anything which blocks testosterone in any form, even its breakdown, presents a threat to the anabolic pathway. Therefore, bodybuilders shun this drug and use Rogaine only. It is interesting though. Is it ignorance? Or just paranoia? I think their concern is that finasteride will block the effects of all the illegal steroids they're taking, is what's really going on. But interesting.