Majoru Oakheart
Adventurer
It's not just that. The number of people who take 1 level of Sorcerer for their Fighter so they can cast True Strike or Shield is amazing.I disagree. Multi-class only between base classes and you won't do anything more broken than you could while single-classing. It's PrCs that are broken. I only use them like originally intended - as options I offer when PCs have joined an organization in game (or more generally done something plot related, they don't know if doing it enables a PrC or which).
I knew a Wizard who took one level of Rogue just to get trapfinding and the Rogue skills as class skills. He then used his really high intelligence to take all of the Rogue skills. It was a Living Greyhawk character, so he played with many different groups. But his Search skill in order to find traps was better than every Rogue he ever encountered. And the rest of his Rogue skills were on par or better than them. So, he tended to make Rogues feel useless.
Fighters with one level of Barbarian are way better than Fighters without it. Especially when you can just take a feat to increase the number of Rages per day you have.
There are many other examples. Being single classed in 3.5e was unoptimal.