Yes, it will make the difference between being gluten-free and being not gluten-free. Yes, we know the addages, "All things in moderation," but it doesn't apply to gluten. Even small amounts of gluten can cause the intestinal damage that sets you at risk for autoimmune diseases and imbalance of gut bacteria. Just slay the gluten beast.
what is it about the sandwich that you like so much?? you could try eating other "paleo" foods instead that would remind you of it like a strawberry smoothie with almond butter and coconut milk. make some fruit and nut bars with almonds/pecans and your favorite dried fruit to get that pbj flavor. larabar makes a pbj that tastes just like the real thing but has no grains.
Perhaps make it a once a week treat? Instead of a cornerstone of your diet.
If your goal is to follow a paleo diet, bread, a legume spread, and a sugar spread is not the best way to do it.
If you are generally healthy and enjoy this, you can certainly eat it without getting sick.
If you want a paleo version, make blackberry jam with stevia, almond butter with maple syrup, and serve on a but loaf.
Won't be healthier, but you will totally be paleo
Today it is super thin bread, next time you start going for the middle sized slices and before you know it you are stuffing in whole loaves of wheat bread. Some people can do small cheats and keep with the plan and others like me would fail miserably and start eating wheat and other junk.
You totally can't hang out in the paleo treehouse clubhouse eating PB&Js.
Depends on your personal situation...
are you fat? thin? in shape? a couch potato? metabolcally healthy? pre-diabetic? T2? T1? Autoimmune issues? one per month? per week? How much J?
Kinda hard to give a decent answer in an information vacuum......
simple answer, in most cases a small PB&J won't do much to derail your paleo efforts