In the eyes of the law, until you're actually married, you're not necessarily automatically an equal parent (e.g. the father of a newborn wouldn't be allowed to register the birth alone if he isn't married to the mother). That said, they're unlikely to question you since, as PP have said, they won't know of your wife's objections.
However, PP are saying that you are an equal parent to your wife, which of course you are; but this also means that SHE is an equal parent to YOU. Your opinions on things relating to your son (unless illegal, of course) matter no more and no less than hers.
Unfortunately, there are some things over which no half-way compromise is possible - unless you come to an agreement, one of you gets your way and the other has to lump it. How would you feel down the line if, say, she was dead-set on having another child and you definitely didn't want one? Or if you set your heart on moving to New York and she insisted on staying in York?
If you go ahead with it without telling her in advance, you will have got your way, but at what cost? You will have 'won' this one, but she will never completely feel able to trust you in anything again - never a good background for a continuing healthy relationship/marriage.
You really must discuss this and any other potentially controversial opinions/concerns with her at length before doing anything unilaterally that you know or suspect she will strongly disagree with. On some things in your lives together and as a family, one of you may end up having to give way to the other's preference - but never before you've discussed it fully and clearly agreed on what you're going to do.