Sure, if, by "theory" you mean "outlandish idea someone made up without any basis in fact and might as well have pulled it out of their ass" ("just a theory") instead of "systematic framework of ideas intended to account for, explain and relate together a wide amount of existing observational and experimental data, and to predict the outcome of similar results in the same field in the future" ("scientific theory").

"Like cures like, and weaker is stronger" was not a "theory". It was a wild-ass guess which also turned out to be fantastically wrong. The thing that made homoeopathy practitioners think it worked was bad (non-blinded) patient experimentation, where things like the observer effect, confirmation bias, the placebo effect, regression to the mean, and a whole bunch of other psychological biases, all came (and still come) into play.