I didn't downvote -- it's fair to be skeptical that a machine that spends hours making loud whirring noises would be more efficient than just scrubbing some dishes in the sink. And I don't want to careful about making unequivocal statements like "dishwashers are always more efficient", I've just heard some convincing reasons why dishwashers in particular are pretty cool and (unintuitively) efficient.

In my observation unfair downvotes come, when people are angry at something and looking at anything that looks like a scapegoat to direct that anger, which can be anyone not expressing the same mindset they have. Which was you by asking that question that apparently was enough to mentally puts you in the "stupid treehugger camp". I would not worry about it too much and try to not take it personal.

Their rational explanation is probably "how you can be so stupid for not knowing that common knowledge".

And well, even though I am indeed a treehugger, I also knew about the efficency of dishwashers before and also assumed it to be common knowledge, but I would never downvote someone because of a genuine question adding to the conversation.