Why did Samson's parents object to the woman he wanted to marry?

Answer: She was a Philistine

His parents asked, "Must you go to the uncircumcised Philistines to get a wife?" But Samson said, "Get her for me."

“One day Samson went down to Timnah, where he saw a young Philistine woman.”— Judges 14:1 (BSB)