I think it is normal for a man not to desire children. For all the reasons you list. It is also normal not to want to get married, for many reasons all talked about here often. But, when you fall in love that all changes. Suddenly marriage doesn't sound that bad because the thought of living the rest of your life without "her" seems so much worse.
Having a child can't be explained until you have one. It is like having a great puppy only x 1,000.
The love comes with the caring for the child who is dependent on you for 100% of everything. The more you hold, care for, feed, play with....the more you fall in love. A child is magical, they are your hope for the future.
It doesn't matter if the child is yours or not, they have a "light" a glow, their smile and laugh will melt the coldest of hearts. Their innocence, their desire to learn things is intoxication.
The ability to relive all your childhood joys, like Christmas, the Zoo, sports, camping, Disney land?.....all hold a new excitement through the eyes of a child.
Women instinctively know all these things, or they would never want to be pregnant.
Trust your wife, this will add to your lives, and look on the bright side, a pregnant wife is a drag for you and her and leaves permanent damage, (often).
Your fear is normal, millions of men have taken the same path and been rewarded by having their hearts opened up in a way they never regret.