There is a rather large economic rent attached to HFT at the moment. If my project or others like it can eat into that rent a touch, it might not stay that way.
Exactly, if you take the position that gains from HFT are basically "stolen" profits from otherwise more productive market participants, then any that can be "stolen back" is a win.
There have always been "market-makers" why do you care if they are algorithmic or human ?