I think the strongest argument for using small words, simpler sentence structures, etc, is that many EAs aren't native English speakers. Using simpler language makes the posts more accessible to them. That said, Google Translate and other forms of machine translation are becoming increasingly good, so I wouldn't be surprised if that particular problem fixes itself in 1-3 years.

That said, I think your third point is plausible, but the first two are less so. 

1. I don't think big words are less respectful than small words. If anything, you might expect the opposite effect (small words sometimes sound condescending). By default, I assume my audience is literate^[1], and I think this is more respectful than dumbing down. 
2. I think it's easier to screw up with small words than big words, because small words tend to have multiple meanings for the same word, whereas big words (in general) tend to have more precise and isolated meanings.
   1. Consider "good" vs "highest EV" or "tiny" vs "nanometer" 
   2. (If there are studies where big words are more likely to be misleading, even among a reasonably selective audience, I'm willing to be corrected).

1. ^{^}

   When I conducted a Twitter poll of what my follower's reading SAT (an American college entrance test) scores are, of the people who took the SAT, ~1/3 of followers claimed to have the highest possible score, and ~1/2 of followers claimed to have a score in the 99th percentile. Now, it is very possible that those people were lying. But if you lie about how good you are at reading, dumbing down my word choices probably wouldn't make you feel more respected.

Sounds good, especially when you want to write blog posts for worldbuilders who don't have a lot of specialised knowledge.

Here is an example I wrote about city agriculture after an energy decline. Maybe I could use this strategy to write worldbuilding blog posts?

Food and water

People couldn't trade food over long distances. So they ate food grown nearby. Everyone grew crops and took care of them. They grew food forests in parks and boulevards. These forests had fruit and nut trees, shrubs, veggies, herbs.

People prunned weeds. They kept calendars for sawing and harvesting. They catched rain in containers. They weaned the grains and stored them indoors. They made manure. They kept chickens and other birds inside. They grew copiced trees in their parks and boulevards. And they cut their branches.

People used stationary bicycles to power electric stoves. Others used solar stoves. Yet others used camping stoves. They cooked fresh or nonperishable food. Meat was rare.

People socialized while cooking. They also cooked in community kitchens. These kitchens were in appartment buildings or restaurants. Kids played, friends talked, neighbors banqueted.

People moved water from rivers through channels. Or they took it by hand. They purified the water at home. They flushed waste down the toilet. Or they made manure. They sold manure to villagers. People used toilet waste in fish ponds. Algae multiplied and fish ate the algae. People then fished them.

By the way, this was grade 5 level text, so no wonder it's that simple.

People also say "expain this to a 11 year-old and you'll understand this". It seems like this Hemingway app is useful for the Feynman technique.

Some good advice here, but I don't think it applies universally. I like forum posts that use (correct) technical language when it conveys important information, and I think some of the best forum posts are dense and carefully-argued. I think some amount of jargon is okay too, though probably worth trying to avoid.