The down arrow makes voting pretty much impossible on mobile devices. Can I get 18 downvotes here so my karma will be below 500 and I won't have to put up with the down arrow anymore?

There are various HN interfaces people have written specifically for mobile. There's http://hckrn.ws/ and http://ihackernews.com/ for starters.

A quick google search reveals https://itunes.apple.com/us/app/news-yc/id434787119?mt=8 for iOS, which includes a "confirm votes" toggle setting. There's https://play.google.com/store/apps/details?id=com.rickylaish... for android as well.