thetwocultures I think in light of the fact it seems your parents may be at fault and that you and your partner have a child together that you have a clear opportunity to support your partner. An opportunity to accept he does not want to socialize with your parents.
Presumably you made a choice to start a family with your dp and this should be where your loyalty lies, IMHO, unless your partner is actually 'in the wrong'.
In your shoes I might 're think the wedding, unless it is fully planned, and maybe get actually married in a quiet ceremony somewhere. Or travel to a beautiful location with your partner, son and maybe a few close friends.
Then have a big family party at home. I have no idea how your partner or his family would feel about this. But it would mean your special day was not 'tainted' by the lack of family comfort.
The wedding is one day, family events and birthdays are what you make them.
My brother in law never visited my parents with my sister and their kids as he was allergic to the cat!
My sister used to say she felt like a single parent when she took her kids to see my parents of course!
Now, years later, our parents are both gone (so is the cat) but our husbands and children are very much here.
When you marry/have a child or even move in together you make a new family.
If you love him, choose him fully and accept time with your parents will not include him.
If that is your heart's desire go for it and defend it and stop trying to change him.