Agreed. There's a lot of possibilities regarding contraception and every situation is different.I've used the calendar based method combined with the person pulling out when I was in a monogamous relationship with a man and it worked for me but I wouldn't recommend it to everyone..
A lot of guys don't know when to pull out and some guys who refuse to use condoms will just not pull out. (Which is an assault) Also a lot of factors can modify someone's cycle and even if you're super regular if the guy doesn't pull out what if one month you're not feeling well and stress, weight gain or loss, changes in diet, new medication etc messes up your cycle?
I just think it's too bad that we load women with synthetic hormones that often mess them up, when we could technically accomplish the desired goal only with a piece of rubber–if some men were not so peculiar.