My 26 year old pregnant daughter is getting married. Who pays for wedding?

I believe that if she and her boyfriend are "adult" enough to live together and make a baby, they are "adult" enough to pay for their own wedding. My ex-wife believes as father-of-the-bride, I should pay. I do not in any way condone nor support what they did; living together and getting pregnant pre-marriage; and worry that if I pay for the wedding, I will be sending the wrong message to my two younger daughters that I support this behavior. What should I do; stand my moral ground or pay for the wedding?