Discussing who's a Christian and who's not will always be full of competing motives for just about anyone. i think making any progress in these matters requires a lot of self-examination and prayer to keep our motives and aims pure in the matter.
We may try to favor certain boundary-markers because it works in our favor--certain boundary-markers leave us feeling sure of our salvation and the salvation of some or all dear to us. The other side of that coin: i think we'll have a natural tendency to resist strongly certain boundary-markers because they exclude us or those we love and we don't want to accept that insecurity. "Well, that just can't be right because that'd mean my dear sweet grandfather is in hell." Does the fact that my grandfather was dear and sweet to me obligate God to keep him out of hell?
Just as tempting can be the motivation to keep certain people out of the circle. Maybe there's someone we perceive as having done something unforgiveable or unacceptable or having wronged us so horrifically that we thirst for justice in the matter. Thus, we strongly resist any boundary-markers that might seem to include them or make it easy for them to get inside the circle. "Well, that just can't be right, because that'd mean so-n-so who wrong my family so many years ago is just fine now." Does my disdain and unwillingness to forgive someone obligate God to bear a grudge against that person as well?
i must be honest with myself about what i'm after--what i want? or what God wants? What if God leaves people out whom i want in? What if God allows in people whom i want out? Will i fault Him? Do i know better than God who should be on which side of the line? The truth is, if God leaves out someone i wish were in, God must know better than me about that person or about why certain boundary-markers are necessary. The truth is, if God allows in someone i wish were out, God must know better than me about that person or about why certain boundary-markers are where they are. Thus, at base, i ought to strive to wish for God to prevail in each case even when it conflicts with my personal wishes.
Most recently in my experiences, i'm feeling more obligation to resist the worldly pull toward relativism and the line that goes something like: "well, we're all fallible so we could all be wrong, thus no one has any right or place to insist on standing up for anything." It would be very easy to go along with these notions that are fairly common among Christians my age, and i could fit in far more easily with them if i did go along. And sometimes it's tempting. But i must, instead, listen to my conscience and aim to side with God even if that isolates me or upsets others.