What is etiquette?
Etiquette, at its base, is fairly simple. It is the idea that one thinks about others before oneself and treats them well. Be polite and grateful. Follow the golden rule: Do unto others as you want them to do unto you.
This is my day. Why do I need to worry about what others think?
First, it stops being your (and FI's) day as soon as you involve other people. Like everything else in life, once others are involved, they should also be kept in mind. Second, your guests are your friends and family (or the friends of your family). These people are important to you. You would treat them well at all other times. Why not now?
Why are there so many rules? All I see on here is "you can't do this," and "you can't do that."
This goes back to treating others well. There are certain actions that are not treating others well. For example, treating your guests like ATMs or gift dispensaries instead of like your nearest and dearest is not treating them well. Demanding that people use their own time and money to throw you parties is not treating them well. Hosting your guests properly and thanking people who took time out of their busy schedules or lovingly sent you a gift is treating people well.
Our wedding is going to be offbeat/kooky/unique. We're going to do things differently, so the rules are different for us.
There is a huge amount of flexibility in what you can do for your wedding while staying within etiquette. Many people on these boards planned or are planning weddings that are not strictly traditional, but these weddings are still etiquette-okay because guests are being taken into consideration. Some of your offbeat/kooky/unique ideas might not fly, but plenty will.
My mom/dad/cousin/Rando on the train says that I have to XYZ at my wedding. It's 2014. We don't have to follow their outdated etiquette rules!
Many of the "have tos" that are passed around are traditions, not etiquette. Wedding traditions are behaviors or rituals that have been passed down within a social group. If they do not affect your guests, they do not need to be followed.
Tradition vs. etiquette:
-You must have the same number of bridesmaids and groomsmen. vs. If you choose to have any wedding party members, choose them because you want them; people are important because of who they are, not because they make the sides even.
-You must have a big evening reception. vs. Wedding receptions can be any size or at any time of day, so long as everyone invited to the ceremony is invited to the reception and it is properly hosted for that time of day; the reception is a thank you for attending the ceremony.
-Second-time brides cannot wear white. vs. Any bride can wear any color; it does not affect anyone else.
-The couple cannot see one another before the bride is walking down the aisle. vs. The couple can see one another at any point in the day that they choose; it does not affect anyone else.
The people who really care about me/us won't care if we follow etiquette. They will come anyway.
Yes, they probably will come anyway, even if they are treated poorly. People will bend over backwards for someone who is getting married. Many people will not mention if they are uncomfortable, hurt, or upset when they are treated poorly by a bride or groom. There are plenty of stories in the Worst Weddings thread about guests who have come, smiled, and endured.