Considering the cost involved and the fact there are already two systems in orbit with existing support, this seems like reinventing the wheel. Mobile phones and other devices support both the Russian GLONASS and American GPS, so why bother with a third?
The official site doesn't seem to offer any reason - talk of "Guiding blinds in an unknown city, locate people lost at sea with a 3 meters accuracy", claims that selling receivers will generate EUR90b of revenue - which of these is not possible now, without launching more satellites?
The one argument with any factual basis seems to be that GPS and GLONASS could theoretically be reduced in future warzones (though in fact the opposite happened in previous conflicts, with the US boosting the accuracy of unencrypted GPS so troops could use easily-available civilian receivers more effectively). None of that is relevant to civilian applications, though: if I do find myself driving through a warzone, whether my smartphone map can locate me is the least of my problems! (Not to mention that surely switching GPS off would go hand in hand with jamming any alternative signal anyway, otherwise shutting off GPS would be pointless.)
The "commercial" DRM-encrypted signals of Galileo bug me, too - I cheered when GPS 'Selective Availability' was turned off, seeing our taxes poured into re-implementing it is hardly welcome.