I don't buy this either/or you are trying to set up. I know lots of people that have big families, in part because they think it's the right thing to do, and also because it is awesome and fulfilling.
"My only purpose in existence is to breed." -- a miserable person unfamiliar with any major pro-family religious tradition.
"I was meant for parenthood and I am doing what I was made to do." -- a happy person who has embraced a pro-family religious tradition.
The difference in the language is that the first one denies a person's humanity while the second one celebrates it.
HAHAHA!! Laughed so hard at the section I bolded. I am: one of 4 kids. The difference being, my parents didn't have us all because they're religious, they had us (and let us know they had us) because they wanted a big, awesome family. My best friend growing up was one of 11 kids. Neither parent was happy, either with so many kids ("mouths to feed"), nor were they happy with each other because the constant stress of so many kids was too much for their relationship. However, being good Catholics, they will never divorce because that's a sin. I still see them sometimes. They look far older than they should, and they rarely smile. Almost none of their children has embraced their philosophy on breeding, and I can understand why.
I also grew up in an area with a LOT of Mormon and Catholic families. With very few exceptions, at least one partner in the couple was miserable and felt trapped by their religiously defined roles, whether they cared to voice their dissatisfaction or not. (And yes, it can be quite obvious to bystanders.) Maybe the husband wanted to stay home but had to be The Provider. The mom wanted to work but had to do too much domestic labor, spent too much time pregnant and raising children to advance in a career. If the husband/religion even let her work outside the home.
The happy families I knew? They all would agree with your second statement. But that wasn't the majority.
I really don't have a problem with people having large families because that's what they want to do. More power to you! I DO have a problem with using religion as a reason to do so, because it's inevitably tied up with misogyny and keeping women from having options. It's that someone outside of the family is defining their choices for them, and using fear of God as a reason. That's a shitty thing to do to another human being, and it's always, always men who benefit from that status quo.
I will also never consider it "pro-family" to have someone who's not part of the family unit define what you should and should not do, or what's best for your family, even if it's your religion telling you what to do. It's your family, you get to decide what's best.
Lastly, it is the ultimate acknowledgement of one's humanity to point out that they have a choice in whether or not to produce offspring. One of the amazing, wonderful things which differentiates humans from other animals is that we have used our brains to give ourselves many choices: choices in how we live, where we live, and how many children we have. And for good reason! Do not forget that childbearing is still painful and dangerous for women, even in the first world and with the best medical technologies available. Things still go wrong far too often.
Frankly, I'd be seriously pissed off at any god who made us to have the sole, or at least overriding, purpose of continuing the species. What a crappy reason for existence. No, I think we have such large brains because we are capable of doing so much more. Do not get me wrong, becoming a mother was one of the best things I've ever done. However, you will never convince me that that is my purpose in life. There's so much more to me and my life than just that. Is it wrong of me to be sad for others who've been convinced to sell their idea of themselves so short?