Your mighty hero has journeyd through dungeons for days, found countless treasures and fought a powerful dragon at the end of the dungeon for about 2 hours straight. But now he feels a certain pressure at the end of his bowels and craps his pants. Understandable, he hasn't been to a toilet for more than two days now.
This is not what happens in most CRPGs. Yet it is what would realistically happen.
But would it be fun? Having to go to the toilet regularly to prevent your hero from pooping/peeing his pants? No. Not really.
This is a very popular argument among people who don't like too much realism like having to eat and drink. They say "so you want the game to be realistic? Then you would also like the necessity of going to the toilet and that's just tedious and not fun."
Well yeah, it's not if all these necessities boil down to Ultima 7's character feeding. "Avatar, I am hungry!", say your companions and you have to go to the inventory, select an item of food and feed it to the hungry character. I've also tried an Oblivion mod that does the same, but it's just as tedious. You hear your character's stomach grumble, then you have to select an item of food from the inventory and eat it. So what's the problem about those two systems? They require manual labour. I call it labour because it's not fun, just a tedious element of gameplay that doesn't really add anything. Another problem is that your character(s) get hungry too quickly so you have to repeat clicking on food all the time.
Now, roguelikes usually have hunger as an element, too. But it's no that bad in those games. You always have a "hunger" stat that is easy to check (like in ADOM, where your current hunger level is at the bottom of the game window) and satisfying your hunger takes two keystrokes at most. Press E, then pick an item of food. And since in roguelikes, food is scarce and you travel through a dangerous environment, it actually adds a layer of survival to the game. In Ultima 7 you could buy food in almost every town, it was relatively cheap and you could fill your backpack with it. It's very unlikely for you to ever run out of food since there's always enough of it around. That's why the hunger element doesn't add anything to the gameplay in Ultima 7, while in roguelikes it does.
Another great example is Realms of Arkania. You could catch diseases easily and had to eat, but not while in a dungeon or town. The survival elements were mostly restricted to traveling. Your rangers could go search for food in the wilderness. It was all about strategic planning: bring enough food and warm clothes with you so you don't starve/get sick, or have a character with you who can provide food when in the wilderness. It wasn't about tedious micromanagement but about planning, which made it fun.
As you can see, realism doesn't necessarily mean tedium. If done well, it can add a lot to the game. But the need to feed isn't the only element of realism you can add to RPGs. What about combat? Hitpoints are sure unrealistic! Well, you can use a wound-system or put more emphasis on (destructible) armour. There are always ways to add more realism to a game without making it non-fun. Most people say "If you want realistic combat you'd die in 5 seconds!!" but no, it's possible to design more realistic combat without making it too unforgiving and non-fun. Jagged Alliance 2, while still hitpoint-based, did it pretty well in my opinion. Getting wounded means you'll lose hitpoints each round until you bandage the wound, which makes it important to have a character who knows how to use a medkit. Not being able to regenerate lost HP during combat makes tactical decisions more important and doesn't let the player abuse health potions/stimpacks/medkits.
As you can see, realism can also be implemented in a fun way. I, for one, am in favour of more realism as long as it's done well. I don't like having to micro-manage feeding my party members when they're hungry because they can't do it by themselves, but I do like having to pack enough provisions for a long travel. Realism can be fun and add some complexity to a game, and I'd really love seeing more RPGs implementing realistic features in a good way.