I refuse to spank and my MIL blames everything on our refusal to spank

My husband and I were both spanked as children and we are breaking the cycle. I grew up in a religious household that believed "sparing the rod spoiled the child". My husband grew up in a household that believed spanking taught good behavior and "kids act the way they do because they aren't spanked anymore". Apparently none of husband's siblings misbehaved since they were all spanked immediately "and never did it again".

Our parents are not allowed to be around our children unsupervised because we don't 100% trust them not to spank them. My husband and I have a daughter who is 3. She has some BIG emotions but she is very well-behaved for the most part. The other day we went for dinner with my in-laws. My daughter didn't eat all her dinner but she still wanted dessert. My husband and I said ok, that's fine. It was two cookies and she ate most of her dinner. She's not a fan of carrots but she ate 3/4 of them anyway. We weren't able to substitute her carrots for something else and she did a great job dealing with the disappointment of that.

My daughter was upset that she could only have 2 cookies when she saw my mother-in-law's big dessert. We explained to her that dessert is a treat and if she's still hungry, she needs more food. She whined but then decided to finish her carrots. My mother-in-law of course said something like "Oh if you had cleared your plate like me, you'd have this big dessert too". I told my daughter that's not true and that her dessert was two cookies whether she finished her meal or not. My daughter was then a bit better and started colouring. I thought it was over and done with but no...

My MIL had to share her opinion which was that she never would have given her cookies in the first place because her plate wasn't cleared. The moment she started whining, she would have spanked her until she stopped whining and then taken her home.

My husband and I said something like well it's a good thing she's our daughter and not yours. We were then read the riot act and told how we were raising a child who would challenge everything so we paid and left.

I guess we're just wondering if it's worth it to continue to try and foster a relationship with his parents when every little thing our daughter does that's "wrong" comes down to us not spanking. We've talked with them and asked them not to mention spanking but they always do.