The original posed the question as if those are the only two options. Because, since there are no bidets that also shoot soap (at least not that I've seen anywhere), those are the only two options.

Then coming in and saying yeah well what about soap is irrelevant. Making it a fallacy. It's as if two people were arguing if salt or pepper is better to use on cooking food and then you came in and said yeah well there's actually a lot of seasonings you can use instead of just salt and pepper. Great, we know that but that's not what we were arguing as we only have salt and pepper.