I have anxiety, and nothing seems to trigger that as much as asking someone to take a picture of the family*. Fortunately Mrs. Cool has no problem asking anyone to help us out. Also fortunately she has figured out to not necessarily ask the first person who walks by, as that person might not be the friendliest, most accommodating, or best photographer. And yes, if you can find someone who is trying to take their own family picture, it is a good bet they will be more than happy to take your picture if you take theirs.
*I just realized I never feel bothered if someone asks me to take their picture. I have even volunteered on occasion when I think a family might want a picture but has to have someone actually snap the pic.
I cannot recall the last time I took a selfie. Or had a picture taken of just myself, for that matter.