I find that a lot of non-runners have little concept of what it's actually like to run an X minute mile. I have had occasional non-runners remark to me "Hey, if you train so hard, how come you can only run 8 minutes a mile?", or something like that. If they're willing to listen, I may politely advise them as to how much training is realistically needed to crank out 8 min miles on a regular basis. If they're not willing to listen, I'll usually just change the subject.

As for people who are obviously out of shape but claim they could easily outrun me (or run some unrealistically long distance) with minimal or no training, I don't try to compare them to me. Usually they're fairly macho types who can't conceive that a 55 year old female could possibly outrun them, so I'd be wasting my breath trying to convince them otherwise. Instead, I try to be objective and recommend an upcoming local race that they might want to consider entering. Of course, they never enter, but that's not my problem (LOL).

You have to be at peace with yourself, not any one else!

Good point...it is a difficult balance to encourage efforts while also feeling the responsibility to talk about the level of commitment that is required.  That might well explain why some runners have been labeled as "arrogant or aloof", when in fact, they are just being realistic or cautious in providing advice to others. 

It really concerns me when I hear someone say, for example, that they are going straight from a 5k to a half or a full.  Also, as you elude to, then some tend to abandon running altogether because there was no comprehension of adequate training, so the race experience was, (quite predictably) miserable. 

I recently met a woman who completed a half and said she would never run again.  I asked why and she said:  "A crazy friend talked me into it."  I further inquired about her training for the event and she said:  "I jogged around the lake a couple of times."   I felt bad for her and wanted to offer some hopeful words, but then she just continued about how it was the worst event of her life...so sad and so obvious. 

I am glad that you started this conversation, perhaps we need to do better about expressing the obstacles and rewards in a more diplomatic fashion?  It is still a dilemma and a great discussion for any new options. 

I really do not see the need to become and apologist, advocate, or evangelist to the sport of running.

I'll answer questions if asked, and I really do not care if people "get it" or not.

Running is an a self-motivated, individual sport. Whether people like it, hate it, appreciate it, or don't -- it matters nothing.