Have not really thought how it might impact upon charity, but I can imagine that someone "liking" a subject on social media or signing up for an online poll might possibly sit back and think they have now done their bit.
And it is that lack of engagement that means that an electronic poll needs to have a really sizeable number of signatories for it to even begin to be taken seriously by politicians, whose inclination might be to just dismiss the sentiments out of hand...
But while these might be considered the downside of a more transparent, connected online world, such e-activism also has a positive bonus of introducing causes and issues to a much greater audience and has the potential of generating greater real world activism. The "Arab Spring" protests, especially in Egypt attest to that.
You might even consider the co-ordination of people involved in the Summer of 2012 UK riots a negative aspect of online activism, since many of those co-ordinated their efforts via online activity....