You can just hide the Comments panel.
Don't know it downloading comment can be disabled somehow (certainly not in LR interface).
I know I can hide the window. The problem is that the comments are just cluttering the database with useless info. And it takes time. Would be nice to have a switch to turn downloadiing off.
This would have to be done in the publish service plugin. It would be reasonably easy to add a flag in the service that opts out of certain features supported by the remote API, like comments and ratings.
In a pinch you could grab the Flickr.lrdevplugin and comment out the calls to FlickrAPI.getComments() and install this as an update to the Flickr service plugin.
For those who are not sure how that would be done (like me), can you provide elaborated information?