You know I think its statement that has many meaning.
First, I think people say Leica killer to acknowledge the quality produced by the system and insinuate that a Leica killer is a camera that approaches the IQ of the Leica system while being considerably cheaper and possessing a similar form factor. It produced the first full frame "mirrorless" camera, and this genre of camera seems to be the one type the interwebs wants more than anything. (Let's see if people put their money where their mouth is)
Its same with Corvette and GT-R fans. They call those cars Ferrari killers because they offer similar performance for a fraction of the cost, and in some categories outperform a ferrari. However, journalist invariably write about the experience of driving a Ferrari, and invariably a corvette and GT-R do not provide the same experience.
Leica sells an experience too. The rangefinder experience. The mystique of Henri Cartier Bresson and others.
Second, it seems that people show real animosity towards Leica products due to the cost of the system and the "collectible" variants that are released for princely sums. Lets admit that Leica has a mystique about its name, and it is a name that every hobbyist will eventually learn; upon learning of the Leica name they learn about the Leica price. This leads to bitterness and envy because the price of admission is way too high. Furthermore, Leica has moved to positioning itself as a luxury brand; all luxury brands are envied by many common people (people have shot each other over starter jackets). Its natural to see how the animosity towards Leica forms in the collective voice of the interwebs because Leica has positioned itself in the "if you gotta ask, you can't afford it" realm of the market.
People want the best, but when the best prices itself exorbitantly above the rest, people will clamor for a "killer" to dethrone the king and give access to best.
