I guess the question is this: Do you think that attitude has a chance of changing? (I'm assuming your context is romantic relationships rather than platonic. Platonic you can give a little more leeway to.) I would say it is as much (or more) about them accepting themselves as it is about them accepting you...and self acceptance, is often not a short road. They may not even want to see themselves differently, much less allow others to see them that way....now or ever.
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I have a friend who has been out for quite some time. She would often hear that same line from men ('not in public') after disclosure. The problem is that just about all of them wanted her to be the 'woman on the side' or their 'dirty little secret' or 'booty call'. They wanted to have sex with someone that had a penis, but not be seen as gay. A few even did social things with her occasionally (though, again, not in the local public scene). But one thing that was universal was that they weren't looking for a full relationship with her, they were just leading her along and using her at their convenience. That is something I see as demeaning.
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I don't know the situation you're dealing with, or if the person is worth a little good faith or not...but I'm very skeptical, as every time I've heard of that line being used...the person isn't working toward acceptance of you and themselves...they're just trying to work you over and get what they want. (of course, if you both want that, and don't care about a relationship, none of this really matters)
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So, "where do we cross the line in compromising", and help "ease [others] into accepting our full identities authentically?" My line would be crossed as soon as someone asked/expected me to hide my authentic self. If I knew them IRL as an acquaintance, I might meet them a couple of times (in a purely platonic sense) to see how they felt, and to see if there was any hope of that changing. If this is some online person you've never met, I'd say don't meet them privately. It may not be safe. Overall, if someone expects you to hide in order to be in their life, they don't have your best interests at heart.