It seems to me that the difference between people who like rules vs. don't like rules is that some want to make the relationship expectations explicit (for various reasons) and some want to keep them implicit (for various reasons).
GalaGirl has a point that making expectations explicit helps keep everyone on the same page. The point is not to bind your partner to a code of behavior - the point is to be up-front about what you want so your partner isn't kept guessing.
Now if your rules are very basic, it may be unnecessary. However, some people want to take no chances and have them anyway. Either way is legitimate.
I hate forcibly-imposed rules, but I have reasonable guidelines that anyone who gets intimately involved with me needs to abide by, for my own emotional and physical safety (and theirs too).
Even something as simple as "treat me with respect" has wildly different meanings to different people because the word "respect" has different definitions for everyone.
^THIS SO MUCH. And it makes it very confusing when people EXPECT you to know how to behave respectfully (or kindly or fairly) by their definition, but refuse to come out and TELL you what that looks like.