On the contrary, I think not hiding your friend list is unprofessional. I'll get back to that in a second here.
It is well-known that recruiters/HR look through your online life. It is well-documented that people have lost jobs because of what they said or did on social networks. I'm going to go out on a limb here and guess that you are not a hard-core party person (or if you are, don't tell me about it*). As other people have commented, what you do on your own time is generally not the business of your employer. Who your friends are is your business.
I said I'd get back to that thought. Here it is: Who your friend are is your business. If you advertise who you hang out with in your own time, you can be guilty by association. Are you friends people who post questionable political messages? Do they party but you stay at home? If you don't show it, HR won't find it. As long as you don't come to work drunk or high, HR typically doesn't care. What they are looking for when they look through your online life is if you are someone who goes out to party every night. That can be a sign that someone is less reliable. They want to distance themselves from people are "alt-right" (right-wing) or "alt-left" (left-wing). It isn't about you, it's the impact to the company and the brand image that you will be representing.
Anything you post online can be construed as "my employer leans this way politically" or "heyyyyy, i'm up partying all night, they don't care of i come in late."
It's less about having something to hide, and more about keeping you and your friends private. It's none of my business who your friends are, until it impacts me as an employer.