You see it over and over again "Thieves are too weak", "Thieves ruin the play dynamic","Thieves ruin the way the rules are played"... which all ignore the role thieves have played in history, literature, and legend.
Some Thieves: Ali-Baba, Sinbad, Fafhard, Grey Mouser, Bilbo, The Artful Dodger, François Villon, and thousands to grace the pages of The Police Gazette.
The thief has a role defined by reality, history, and legend those that ridicule it's inclusion in RPGs are choosing to ignore a huge swath of our culture.
I saw this this morning "All you need to play a thief is caution, luck, and hit points"...really? So all you need to be a b;blacksmith is a hammer and anvil right? A sword and a suit of mail make you a warrior? Odd those jobs take years of training, so does being a professional thief. Anyone depending on HP to be a successful thief just isn't doing it right.
"The odds of success are too low" ... really what are the odds of you not getting your hands chopped off when you stick them into demon idol on the 4th level of the howling tower of madness? "Thief skills change the nature of the game because because anyone should be able to hide, sneak, search for traps..". Yup, anyone can hide, sneak, or search for traps the thief just does it like a pro. D&D has a generic "sneaking" mechanic built into encounter resolution: the surprise check. Sneaking past a guard, slipping out of an ogre's cave unnoticed,... surprise check. If surprise favors you your act works, you are not required to fight if your foe is surprised... they might not have seen you yet. The thief skills in this regard are on top of that making a "meager" 15 or 20 percent a pretty sweet advantage. With caution and reason anyone can detect a trap and possibly disarm a trap which makes the thieves ability to do it quickly with less risk (as expressed by the thieves skills) pretty cool. Just because a thief is good at something or the bonus doesn't look large doesn't mean it's weak. the criticisms of low level effectiveness are silly: first level fighters are pretty unimpressive fighters, MU's have one spell, clerics don't even have a spell at 1st level in many versions of D&D. Likewise detail and enhanced capacity don't exclude other from attempting a task.
"Thieves ruin the party dynamic and unity, they introduce strife." Thieves disrupt a game when played by jerks, just as fighters, clerics, and magic-users played by jerks ruin the game. Anyone grabbing too much DM "camera-time" to the detriment of everyone else is being a jerk.
"What's a thief doing in a fight anyway?" ... indeed, what's a priest doing in a fight, what's a scholar doing in a fight, what's a knight doing in a fight in the sewers beneath a city... any character in the wrong fight at the wrong time shouldn't be in a fight.
Thieves are real, thieves are a part of our history,literature, and legend. Thieves have a place at the game table.