It's pre birth assessment stuff, they have to ask. They will do a plan before signing you off usually seeing what support you have in place when they step back.
I had a history of medical issues so whatever reason they're there they still have same tick box.
When they ask parenting plans, I think they are checking you can make educated decision and able to safeguard your baby.
They won't take your baby, social is usually there for support. They can help with housing, funding, access to different services and often children with disabilities are under them for support, it's not just the scary stuff.
I know it's worrysome, especially at a vulnerable time, being defensive won't help you, but I understand, whenever you hear "social services" the assumption we all initially make is the bad stuff, I was horrified 😅
Tell them how you feel, I did and the lady reassured me and explained how it worked, the different stages in social care and how to have a child taken its at the highest level, goes through court and your notified of everything. The first stage we were at and I'm guessing you are, it's literally assessing for support so you all thrive and planning for what could go wrong to ensure it doesn't. (My case I get ill and the child's plan during that, and yours if your ex harrases you or comes back and how to ensure your both safe)
I did get discriminated against due to it at one point but they sorted it out straight away and had my back. So do express concerns with them, they are very proactive and hate the brush they are tarred with so will be more then happy to alleviate your worry.