Coeliac disease is much more serious.
For a one-off, no, I don't think it is. Force-feed my brother a sandwich, and he'll have little or no ill-effects from it. Change his diet more permanently, and you've written a different story, but there's certainly no point worrying too hard about crumbs in the butter, albeit they're best avoided as a bit infra-dig.
Same with lactose. I'm not 100% intolerant, just annoyingly so - it's tedious and boring and makes buying ready cooked/made food very difficult although not as difficult as coeliacs have it.
Not sure that he really finds it that hard to be honest - it's just a matter of finding an appropriate routine, especially now that every supermarket has a FreeFrom section.
No egg/wheat/nut/mushroom/shellfish can be entertaining sometimes though - mostly I just give up and cook from scratch.
people who might previously have suffered in silence at home are now feeling they have the right, if not always the ability, to safely eat out.
That's an interesting point. I guess I've not really considered it too much because, growing up, I was never really aware of us not eating out because of my brother's diet. (In truth, the fact that steak and chips is practically universally available meant that there was always a possible option, even if it was sometimes a tedious one.)
More recently, it's been more obvious where some chefs or restaurants simply don't seem to give a monkey's, while others are quite different - going out to a nice place in Edinburgh for one of my parents' birthdays and booking the tasting menu, we supplied an impressively long list of dietary requirements, to be told "that'll be no problem - the chef believes everyone should be able to enjoy the meal equally."
This included suitable homemade bread that was gluten, wheat and egg-free: sadly subsequent visits (for a more modest menu) have revealed that they've started buying in the gluten-free bread, which now contains egg - fine for my brother, not so for my wife.
Still, steak and chips remains the universal panacea - at least unless you're vegetarian ... or a Parisian waiter insists that they haven't wiped the bearnaise sauce off the plate, and that there's no egg in it anyway.