So, the last note was really from the perspective of safe boundaries already in place.
Which, I know, is often not the case.
A lot of the time, the boundary-crossing is just not knowing what the roles and limits are in the new situation. Very common.
But there's also the unsafe boundary crossing, the habitual, dysfunctional, or just plain blind-to-the-issue trampling of one's sense of self and safety into the dirt.
Even when someone is good on boundaries with one person, they may suck with another. My mom does pretty well with boundaries with me (and where she doesn't, I tend to defend mine pretty well), but poorly with some of my sibs, and particularly poorly with one of them. Unfortunately, that's the one who is most likely to be really hurt by the boundary crossing. It's like my mom can't sense where that boundary is, even when she's been told over and over.
She's mainly not great with introverts. The more introverted, the less successful. So that's her blind spot, or the biggest one.
Despite that, she taught the idea and concept of boundaries to me pretty well. I watched as she held her boundaries with her aunt and father, both of whom were only semi-functional people, though in different ways (and both with physiological underpinnings to their issues, making them less responsive to efforts to modify their interactions).
I also watched my dad set boundaries, though his are set so firmly that there's no flex. At the same time as I feel a little sad (and maybe even slightly hurt) that he doesn't let others 'in' beyond that hard line, I also have every reason to respect that choice. He's let people in and had them end up dangers to him - even if it took time for them to go off and send shrapnel flying everywhere. He determined that he was not a good judge of who to let where, so he chose to set boundaries that were hard and firm, and be very cautious about the process of letting someone in - or himself out. He's willing to allow permeable windows now and then, out of regard for those who are asking with love for more from him. It's a tough concession for someone who has been so trespassed upon, and one I value highly.
Setting the boundaries often starts as an act of self-preservation.Sometimes out of desperation, but generally somewhere in the world of 'I love myself enough to protect myself' (or more commonly, I love my child so much I must hold this line for them, even though I've never been able to hold it for myself).
For those becoming whole themselves, the meaning begins to add in 'I am worth protecting, so I will protect myself, too' - a statement of self-love and self-respect.
From there, it matures into a lot more than that. It becomes a statement of values, morals, ethical position. I choose to hold this line because it is right and just that I do so.
And further, it develops into an act of love outwards, as I noted to andrea - choosing to prevent someone else from acting in a way that they might later regret is an act of love. Even if the odds of that person achieving enough healing and wholeness that they get to that place where they might regret former actions might be iffy... even if it is so unlikely as to be monumentally absurd, it is still an act of love for them to prevent them from harming another.
It's akin to taking away the car keys, or escorting one's drunk buddy to a side room to cool down before they get into that fight that is brewing. We know they're not functioning at full power, so we make sure they can't do something stupid or harmful that they'll regret later.
Yeah, it takes knowing them pretty well to know how they'd want it handled, and no, most people would rather not have the answer be 'no contact because any contact leads to disasters'. But at the same time, I know enough recovering alcoholics to know that while making amends is cathartic, it is also heartbreaking. How much better if that incident hadn't happened at all? There's definitely always going to be something that needs healing or making amends, no matter how hard any one individual holds boundaries. The boundaries just prevent it from being worse than that.
So, yes, holding those boundaries is an act of love. Just as my mom refusing to sit still for my great-aunt's horrifying racism was an act of love - my great-aunt really didn't want to be mean, or hurt people's feelings, she just could not comprehend that everyone was really (REALLY) the same inside. (Okay, maybe she was mean, too, but at least with some effort from her loved ones reining her in, she could be remembered as less mean than she'd have been if nobody stopped her.).
My mom taught me the jelly-jar first layer boundary, where you picture a glass jar (as pretty as you'd like) over yourself, nice and sturdy, at the level of your personal space bubble. I personally picture it causing a slight diminishing of sound, as well as preventing physical contact, since I am sensitive to tone of voice. There are plenty of codependency books that can help with boundary-keeping with love - anything from Melody Beattie's classic Codependent No More: How to Stop Controlling Others and Start Caring for Yourself, to the Christian-oriented Love Is a Choice: The Definitive Book on Letting Go of Unhealthy Relationships. There are over 6000 results on the Codependent search results page, so fish around and find one that resonates - quite a number of Christian ones, and a lot of Al-Anon, Codependents Anon, and other 'angles' to choose from! Consider it a holiday gift to your entire family.
All more of the Acceptant, Loving, Faithful rules, when it comes down to it. Acceptant requires allowing them to be where they are without that desperate need to change them. Loving requires acting for all concerned in a loving manner - this doesn't mean being a doormat, it means stepping up to the boundary line to hold it quickly, gently, firmly, so that there isn't so much need to push back violently (though there's no way to guarantee that the other party will respond better, still the faster and firmer we hold the line, the less likely they'll forget where it is). Loving for ourselves, and for them, to do that. And Faithful allows that it is possible for anyone to heal, even if we have no power over that process. They might never succeed, but having some faith in the possibility makes it possible to act with love toward that future state, which then makes it so much easier to protect that whole future self from the actions of the current state - at least where we have power and authority to do so, which is definitely a limited scope. (I think the emphasis on the precious child concept - that everyone deserved to be precious and many of us were not - can make it harder to grasp the precious whole adult image. We're taught to picture ourselves - and others - as our child-self, deserving the love and respect we didn't get. But it is also quite powerful to picture our - and their - whole adult self. It can be heartbreaking when that future state seems improbable in the extreme, but it is an important grief to deal with, and can make it easier to understand our next steps, IMHO, if we can hold both the past and the future as a continuum.)
Sanity demands that first step - that we protect ourselves. Love demands that we protect our kids. And in the end, it is compassion (a form of love) that demands that we protect those who would do harm, by preventing that harm through holding our boundaries clearly and with dignity and pride. Even when they're also held with regret.