Allow a user to like a post without having to log in?

I got into an argument with two people who insisted that users do not have to log in to like a blog post. Is this okay? I'm sorry if it seems a silly question, but I was really concerned with the accuracy of the number of likes if we had to implement it this way. I tried explaining to them that a computer can have multiple users and a user can have multiple devices, but they still insisted, suggesting that we could use cookies or even identify a user using the computer's IP address to determine whether a certain post has already been liked or not. If this is okay, I would love to have someone explain to me why (aside from it removing the hassle of creating an account for the users/visitors of the site). Thank you.