In a church, there should be a higher level of morality and seriousness. It is also up to the hierarchy of that church to set and enforce the guidelines, so it all comes down to "doing what you're allowed to do".
My upcoming wedding will be conducted outside of the church becuse Maureens first wedding ( in a Catholic Church ) was never nullified. When that is done, we will renew our vows and bless the union in our own Parish Church.