"I object to legislation to promote relationships which are obviously unhealthy, dangerous, or harmful to society."

Ake... the word 'obviously' has been correctly pointed out above as HIGHLY debateable, so I will focus on the word 'promote'. A law that allows freedom & latitude in choosing one's relationships and decisions about marriage & child rearing within those relationships is hardly 'promoting' anything.
You have asserted before that various things...(like display posters on buses) promote homosexuality. Those items are designed to be information about where to find medical care, helpful organizations...etc. No one is 'promoting' a particular lifestyle...except those who think like you! It is just NOT obvious that the majority case should be the only case.
The 'straight' lifestyle will always be the majority... that's how most reproduction works. But for those nice, decent, caring people who happen to have been dealt a minority hand in life's card game, adoption and IVF can help provide a happy, meaningful way to participate in society. Children? They are amazingly adaptable.... having 2 mothers or 2 fathers makes little difference if those parents are good and honorable people.... certainly better than 'normal' parents who mistreat, ignore and repress their kids. 'Studies' have shown this!
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Pete...Raggytash makes the point quite well about the necessity of religious trappings for marriage. For those who wish to add the church into their marriage ceremony... fine. But marriage licenses are issued by the state. (We in the US have just had that difference spelled out by the Supreme Court. Sadly, a few very conservative local bureaucrats are refusing to issue marriage licenses based on their own religious beliefs, rather than the status of the applicants. No one is asking a clerk to perform a marriage ceremony, but merely to issue a piece of paper.)