- It's not an ancient practice, it was invented by a failed German Physician in 1796, only just over 200 years ago.
- So what? People in the past were wrong about a lot of things.
The ancient practice argument would be invalid if it were true, but also is just plain wrong. Here's my full post on the history of homeopathy. I suspect the reason that some people attribute homeopathy with a much longer history is that they mistakenly equate it with herbalism, which is a whole different kettle of bullshit, but that parts of which might have at least some basis in truth.
The fallacy at work here is The Appeal to Tradition. To paraphrase Tim Minchin, just because ideas are tenacious it doesn't mean that they're worthy. Our predecessors were wrong about a great many things for a very long time: the earth is at the centre of the universe; powdered tiger penis will make you virile; the universe is only 8000 years old; fires, floods, earthquakes and volcanoes are the acts of angry gods or spirits. The longevity of an idea or practice gives no credence to its veracity. Samuel Hahnemann, the inventor of homeopathy, quit medicine largely because he saw that the practice of bloodletting was killing more than it saved, and bloodletting had been standard practice for nearly every illness for around 2000 years. Among his faults Sam clearly did not count susceptibility to the this particular error of reasoning. The fact is that homeopathy was never properly proven to work in the fist place; the many people since then who have believed homeopathy helped them or others were just as deluded as modern practitioners/patients, and their opinions should not influence us now.