The first question is what you mean by liberal. The three articles include Jewish and “progressive” Christian, and author on a site that doesn't seem to be religious who doesn't identify his brand of Christianity. But what CF considers liberal is typically mainline Christianity, which doesn’t normally go as far as progressives. I’ve been involved in discussions of sexuality for decades, and as a Sunday School teacher I have at least some idea what our kids and parents think. My suggestions are roughly in line with that.
While the second of the three is useful, there are limits.
* You really want people to make decisions on what they are going to do before getting into emotional situations. Maybe this qualifies as rules and maybe it doesn’t. The church has a duty to help people form these decisions. As noted in one article, comprehensive sexual education has proven the most effective way to do that, though I'd expect the Church to couple that with Christian ideas about marriage and sex.
* We need to honor commitments. Deep personal relationships require trust, and trust requires us to make and keep commitments.
There's a whole debate about the usefulness of rules. The extreme position was "situation ethics," which asserted that we shouldn't have any rules, but should in any situation do what is the most loving. This was pretty effectively demolished by Paul Ramsay's book "Deeds and Rules in Christian Ethics." That debate was long enough ago that a lot of Christians today don't remember it.
I’d say that a permanent marriage is the ideal. However as humans, we often don’t get the ideal. Roughly speaking I’d try to stay reasonably close.
Liberal Christians have generally opposed prostitution. De facto both liberal and conservative Christians have sex before marriage. But I think most of us would say that that should occur in committed relationships, and that there should be as few as possible before marriage.
Liberal sexual ethics have typically been stronger than conservative on demanding mutual support. It was really pressure from liberals, Christian and otherwise, that caused both churches and society to seriously deal with abuse in marriage and abuse of children. Liberal ethics have also been stronger in recognizing potentials for abuse caused by differing levels of power or prestige, e.g. sex between student and teacher, or minister and someone they are counseling. These things have been picked up by conservatives.
I think the best definition of ‘liberal’ is classical liberalism. A general tendency towards freedom of expression and doing away with traditional strictures, rules, customs or traditions in favor of new ways of doing things. This is as you have said represented by the mainline Protestant churches in America.
I think that liberal attitude is exhibited in the drifting of attitudes within liberal denominations towards accepting the sexual revolution instead of rejecting it. For instance, when saying Christians generally oppose prostitution, what is the liberal Christian reasoning behind opposing someone’s freedom to purchase sex and someone’s freedom to sell sex? Are they not free to do as they wish or desire? If so why not? If you are going to argue on the basis of power dynamics then what you’re engaged in isn’t so much a theological reckoning of these matters as much as you are a sociological one. More political than it is concerned with theology.
It’s like when you say marriage is an ideal, but not one always lived up to. This effectively does away with the rule or standard of marriage, viewing it as impracticable and not something to be done in reality. It can be aimed for but if we fail to meet it, then what exactly?
Not sure I agree with you about liberal sexual attitudes being stronger in recognizing power dynamics between people. Such dynamics have always been part of society and general wisdom has told people to marry closer to their station. Rules have always been in place to prohibit these sorts of relationships from forming, though not for the reason of power but more for property sakes. Though they achieve the same outcome. Bishops were forbidden for instance to have a woman living in their house as early as the council of Nicaea. I think even John Calvin had to rebuke one of his friends for marrying a much younger woman.
To the actual question of limits you say:
“You really want people to make decisions on what they are going to do before getting into emotional situations. Maybe this qualifies as rules and maybe it doesn’t. The church has a duty to help people form these decisions. As noted in one article, comprehensive sexual education has proven the most effective way to do that, though I'd expect the Church to couple that with Christian ideas about marriage and sex.”
Is the idea then of general counsel but no application of rules or expectations? This seems more therapeutic than anything theologically orientated. The idea of liberals is to guide people to a certain outcome, but if that outcome is not accomplished then what are the consequences? Does the idea of sin ever enter the picture? Can one sin sexually within this therapeutic style of instruction?
“We need to honor commitments. Deep personal relationships require trust, and trust requires us to make and keep commitments.”
What if the commitment is a minor one agreed to by both parties in exchange for mutual sexual gratification? Let’s add that both parties are doing everything responsibly, taking all necessary precautions for physical safety. Is there anything wrong being done?
Commitment by itself would then seem to be almost the same thing as consent.
As a liberal Christian you can only speak for yourself, but how do you view the question of sexual sin?