Aren't traditional tacos often made with fish? That's not something I'd ever want to try. I hate seafood (although I don't begrudge anyone else the right to like it).
Traditional tacos, because they are 'street food', are usually made with whatever is available, and cheap. There are places in Mexico that you don't want to eat the tacos, because what they're made out of is not palatable to non-natives. Here in the US, you're probably going to get something at least edible, if not delicious, even in a traditional restaurant, be it fish, beef, chicken, pork, etc., because of our food sourcing and preparation standards (which ethnic cuisine restaurants often adhere to better than our traditional fare).