Personally I would be happier if people learned the difference between images for print, and images for the web.
You should prepare images for the intended use.
If you post large images with lots of colours, don't use PNG, but if you must because some one needs to print it, then set it as "interlaced" or "progressive"
Only use 24bit PNG if you were going to use a TIFF, and use 8bit PNG as a GIF replacement.
People tend to ignore other people data limits and costs, when they are not as limited.
When browsing on a mobile device I switch off images because it eats my credit like crazy.
As a "general rule of thumb" your desktop resolution is not suitable for web pictures, no matter what it is.
Before you upload to any site, consider using a tool like RIOT.
In full automatic mode you can see the optimisations you should be doing in your other software.