The real reason an author might want to be careful with things like mind-reading is that it will short-circuit a lot of plots, often in non-obvious ways. This is why I tend to stick to low magic settings.
As for religious laws there's another reason, beyond offending the gods, that certain acts may be illegal. Blasphemy, refusing to participate in certain rituals, violating taboos, don't just offend the gods. They are also an offence against the community itself.
Think about how many people feel about flag burning, defacing national monuments, or what have you. Given an age where the state and church is not separate, indeed a temple is a civic monument as much as a religious one. So refusing to honour the gods would be akin to flag burning; e.g. not a good idea if you're a stranger.
That said travellers are actually less likely to get in trouble for violating religious law, than they are for more secular laws. The reason is that if everyone around you is a polytheist, odds are you'll be willing to honour strange foreign gods when you're abroad; after all, what's the harm? So you'll sacrifice a chicken if the locals ask you to, and everything is fine.
Moreover if a town, or area, has a particularly bizarre custom odds are you'll know about it before you get there. People like to talk, especially if they have a story like, "Yeah they'll cut off your left pinkie if you squint at the image of Bokbok on fridays."
Meanwhile customs, tariffs, and assorted legislation is far more likely to get you in trouble. In Rome it was forbidden to carry knives, or to drive carts during the day. Adventurers may not want to drive carts, but they may, accidentally or not, carry their weapons.
In some area processions have absolute right of way, that's generally a no brainer. most people would figure "Okay lots of priests, weird statues, okay better not block their path." Secular or less obvious equivalents may be far more dangerous. In Venice, the heads of state may also have absolute right of way, often with severe penalties for getting in their way. So if your heroes, even accidentally or briefly, block the path of some dignitary they could be in serious trouble. Not just from the law, but also from the powerful dignitary, who may be very upset that someone tries to interfere with his ancient rights.
How about a slap, or a punch in the face? What is the proper response to that? To many fantasy heroes that is a challenge to a duel, or a great and grievous wrong that need to be avenged.
Let's talk about the original Happy Slapper (http://en.wikipedia.org/wiki/Happy_slapping) Lucius Veratius (no there's nothing new under the sun) who liked to go around slapping other Roman citizens. Back in his day the penalty for this was a fine to 25 as, and to make sure he could avoid any bothersome consequences he had a slave walk behind him with a purse, so he could pay the fine on the spot.
So how about that? Have your character walk down the road, minding his own business, when all of a sudden a man appears, slaps them, and has a slave give them 25 copper coins. That would be original if nothing else.
Moreover once the fine was paid that was that, there was no point in taking him to trial, or involve a jury, because he'd paid the penalty in advance. Wise men shrugged, considered him a weirdo, and went on their way.
Later on the law was revoked, in part due to Lucius Veratius' behaviour.
P.S. I've written a three part article on How to make Pagan beliefs more than Christianity with more gods (http://the-norseman.livejournal.com/3150.html) if you're interested in how culture and religion interacted you might enjoy it.
I enjoy the challenge of working with high-magic systems and making them work. Thought-through, it really should involve no more difficulty than SF has plotting around/with high technology. It's unquestioned assumptions that tend to drive things like, "Well, obviously telepathy is perfect." Why should it be?
The reason is that if everyone around you is a polytheist, odds are you'll be willing to honour strange foreign gods when you're abroad; after all, what's the harm?
Er, well, if the stranger is a sincere believer in his own gods, or if she's a monotheist, they might object to honoring other gods. Maybe they wouldn't do it loudly- I get that part of what you're saying- but this question seems to assume that the protagonists in a fantasy story never take religion seriously. Same thing applies to bizarre customs; they might not seem bizarre to the villages around them, so no one might think to warn a stranger.
I like your other suggestions. Thanks for making them.
The reason is that if everyone around you is a polytheist, odds are you'll be willing to honour strange foreign gods when you're abroad; after all, what's the harm?Actually I assume that the protagonists take their religion dead seriously. However there are very few religions that demand exclusive worship, and they are pretty much all monotheist. Thus a devout follower of the Norse gods, or the Greco-Roman gods, or the Celtic gods, or the Russian gods, wouldn't see anything wrong about offering a sacrifice to someone else's gods.
Let's talk monotheists now, there's a reason that the Jews were considered bizarre, but they were protected by how ancient their customs were. Christians on the other hand were a new religion, and they refused to honour the Emperor and the Imperial gods! Both refused to do what everyone else, regardless of culture or creed would do.
Part I of my article series deals with this precise subject. Part II is also relevant, but not directly so.
What I go on about there is the tendency to see Pagan religions as Christianity with more gods, and I think that's offensive to both Christianity and paganism. It's also somewhat misplaced when it comes to pre-Christian religions.
Same thing applies to bizarre customs; they might not seem bizarre to the villages around them, so no one might think to warn a stranger.This is true, but I've seen very few examples of that sort of thing in genuine travel accounts. The ancient world, and the medieval world, was actually fairly close knit. As you begin to travel to a place you begin hearing rumours about it, you begin seeing how customs slowly change, and if you're at all clever you pay attention.
Obviously inattentive travellers, or travellers who have gotten lost in a storm, or fallen out of a castle in the sky, maybe have some serious difficulties. The same goes for people travelling into the boonies; not only won't the locals think to warn them, but there aren't any other travellers to fill them in.