Since I'm in marriage = sex camp, I'm biased.
But following must be taken in account.
1) Bible doesn't have word for sex. It has phrases.
2) Sex is never mentioned directly. So if marriage start with sex, it will never be mentioned directly. This implies we have from phrases used infer that sex has happened and that sex starts marriage
3) There is no alternative mentioned "ceremony" which starts marriage which isn't sexual in nature. You can't provide verses since they don't exist.
4) Direct consequence of 3) is that believer can't even know is he even married since you don't know did you start marriage
5) Without sex = marriage and as consequence of 4) pastors have to invent when marriage start. Well, inventing theology is forbidden. Theology we are supposed to receive from Lord. For proof, find verses forbidding witchcraft, worshipping other gods....
6) Bible don't mention penis, vagina, semen, menstruation or anything connecting with sexual directly. Only in phrases. This supports point 2.
7) Woman can be wife and concubine. One word can have narrower meaning that another. For example, man/woman in comparison in person. Here man/woman has narrower meaning than person
8) Humans being humans like to celebrate. Well, marriage is good reason to throw party as any other. And it makes sense to formalize alliance by making them public
9) Also, making some ceremony public has advantage of giving security to women by implying she is not just being used for sex and that man will stay, especially if she gets pregnant.
10) Presence of such celebration doesn't make marriage. Even Catholic Church understand that keeping virginity after "marriage" in their church is valid reason for divorce. Maybe, because marriage didn't start for real.
11) Dinah is easily explained by 10 and 11. Somebody wanted to make Dinah "honest wife".
12) Seduction as method of getting married won't be looked favourably. Well, people can get married without asking for approval or with someone not approved, so method of seduction will have enemies
13) Seduction per se doesn't provide security. It's well understood by women are gatekeepers of sex and men are gatekeepers of relationship. Seduction doesn't by itself start relationship (one night stands as proof), and being single mother has sucked historically, so men who caused single motherhood wouldn't be welcomed
14) As consequence of 8, 9, 12 and 13 there will always be some societal push to connect marriage starting sex with something else which will cause confusion in some people to think marriage doesn't start with sex
15) Sex and especially children (consequence of sex, so sex again) are that makes marriage marriage. Any other human relationship type does implies relationship having non-sexual character, so why demand that marriage starts with something not essential to marriage (ie anything not sex)?
16) Anyone looking to be married while wanting to not have sex with their married partner is nutcase. This is nicely connecting with 15 which again points to centrality of sex in marriage and total insanity of trying to say that to start marriage requires something not sexual
Saying marriage doesn't start with sex is like saying employment doesn't start with arriving om first work day. Expanded in point 20
17) Humans do require more than just sex. Sex does make easier fulfilment of other needs. However, marriage does makes easier fulfilling other needs which enable sex. This matter because it makes easy to confuse other needs with centrality sex in marriage.
18) It would be shameful to want to get married just to have sex, so people will speak about something else just to avoid shame which will cause situation from 17
19) Since marriage as state blessed institution is totally screwed up, people will find replacement for marriage. Notice how sexual infidelity is so damaging for boyfriend/girlfriend situation which makes such relationships marriage replacement and also points toward point 15
20) Any sensible legal system understand that point of employment contact is exchange of receiving wages for some tasks done for employer. Singing contract isn't point, it's work done for wages. So if contract says work start on 20.5 and worker starts working at 19.5 any reasonable legal system will conclude that de facto contact has started at 19.5.
So if sex is point of marriage and couple starts boinking each other before "official ceremony" by what reasonable logic you can claim they are still unmarried? Well, they are already practicing what makes marriage marriage, so they must be married
21) Since sex is glue keeping marriage together, therefore stopping sex is same as advising divorce. Therefore advising sleeping couple not "officially married" to stop sleeping is in practice same as advising divorce. I thought Christianity is against divorce in general.
