I dont have a girlfriend now. (I have in the past, of course). Here is how I see this question:
As far as the idea of someone else not tickling your girlfriend, and wanting to be protective of her, I completely understand that. Unless it was a very playful and innocent non sexual intent tickle by a family member or friend, I'd feel uncomfortable about that.
It is your peroggative to feel uncomfortable about having others see your girlfriend's feet. For myself, I love women who go barefoot a lot, so as long as I knew my girlfriend or wife was faithful, whether she went barefoot a lot or not would be really up to her. If she enjoyed it, I'd love it. If she didnt like to go barefoot, because of her feet being cold, or just not liking to go barefoot, I would be fine with it as long as her feet were available and bare to pay attention to at the appropriate times. That would be up to her. As far as the idea of not having others see your girlfriend's feet because you dont want others to feel attracted to your girlfriend's feet, I can understand that. For myself, I realize that in summer and by the pool or such, many women wear sandals and go barefoot, and, inevitably, someone at some time is going to see my significant other's feet. As long as the relationship stays faithful, I really dont care what others want to think about her. Heck, in my life, I have had plenty of foot and tickle fantasies with married women of people I know well. There is quite a difference between fantasy, and actually acting something out and cheating. How you feel is your peroggative, and I respect that, but for myself, what shoes my wife wore or where she went barefoot would be up to her. The most important thing to me is that the relationship stays faithful, not who sees her feet.
Mitch