Anand Karaj is one of the few ceremonies that Sikhs have. It means "blissful union". From my understanding, it was established by Guru Ramdas.

The premise of the ceremony is to make a pledge to each other and to Waheguru in front of the Guru Granth Sahib. During the ceremony, the laavan are sung (check the comments to see a link to them). The laavan essentially confirm that be couple are on a joint journey in accepting the message of the Guru Granth Sahib and will strive their best to walk on the other outlined within it.

So it is a very Sikh ceremony. At the least, it requires a commitment from the couple to be good Sikhs.

There are two objections from the people who were against the protests. 1. Not allowing non Sikhs is like excommunication. 2. Allowing bad Sikhs (go drink after the ceremony, etc) but not non Sikhs is hypocritical.

Point 1: no it's not excommunication. It's a standard that any human can meet. Become a Sikh and have your Anand Karaj. No one is be banned.

Point 2: isn't it hypocritical for the non Sikhs to participate in this ceremony? Isn't it hypocritical for the Sikh to participate in this wedding with a non Sikh as well?

"Bad Sikhs" are hard to quantify. But if you still exclusively hold the Guru Granth Sahib as your living Guru, then you absolutely have the right to come in front of it and make the pledge to Waheguru.

My understanding is that the protest arose against the Gurdwara for not upholding the sacredness of this ceremony, not the couple. The gurdwara committee was incompetent in this regard and were probably given a good fees to have this wedding. So the gurdwara put finances above Gurmat.