The first thing that I notice is that the two of you don't appear to be together in this decision yet. That is the first thing you need to conquer!
We made sure we both wanted to do this before taking the first step..REALLY wanted to. We are in the process right now and in my opinion, adoption is a very stressful, emotional and difficult process to go through. You will be on a rollercoaster ride like no other. You will be thoroughly excited one minute, disappointed, confused or scared the next. If you are not going through this process with the same enthusiasm, support and goals, then it could tear you apart.
In addition to the 'ride' that I mentioned, you have to realize that you are going through all this, emotionally and financially with absolutely NO guarantees. Once you are 'accepted' for a placement, you will want to paint the nursery and get it prepared, tell all your friends and family, go shopping, dream of holding this baby in your arms and tucking them in at night...and, in most cases, spend a great deal of money. All of this could be in vain if the placement falls through...and they can and do, even at the last minute.
Your partner is right, you DON'T know what is going to happen. You are relying on strangers to be telling you the complete truth about their history, including medical. There are no guarantees that if the bmom says there has been no drug abuse, or that there aren't any health and/or generic worries, that she is being honest. I sincerely don't want to sound negative about the adoption process and especially about the bmom's who so unselfishly go through this and do what's best for the child, but you HAVE to look at this decision with a very clear view of reality and be prepared for anything. You have to be ready to accept this child who may or may not have inherited 'issues'. You have no guarantees when you have a child biologically either, but at least you know your own history. If you aren't willing to accept and risk the possibility of someone not being honest about theirs, then it's not the right thing for you to do.
Again, if you don't have the proper support from your partner, this could tear you up and ruin your relationship. Make sure you both REALLY wants to do this before you get too emotionally wrapped up in the idea.
By the way, a lot of agencies require that you are married...not all, but many do.
Good luck in whatever decision you make!