I don't think anyone's suggesting that blasphemy is okay, especially to those who believe.
As for those who do not believe and so blaspheme with seeming impunity, knowing it is upsetting to those who do believe... I think they are disrespectful and rude, and I think their actions/words speak volumes about their character. If they don't realize how people of faith might hear their words, that's one thing. But if they do and they say then anyway, then I have little regard for their manners.
I think of them with the same disdain I would to someone who purposely chooses a pork dinner to eat in front of a Muslim, all the while gushing about how tasty it is and how she should try some "just this once". Or someone who sports a "Darwin Fish" on their car to show how clever they are to bastardize a basic symbol of a religion to make a political point about one small non-essential portion of that religion's beliefs.
Socially, blasphemy is rude. Religiously, it could be dangerous. In some countries, it could cost more than just dirty looks.
But does it actually affect God? No. It affects how we relate to God, as someone so clearly said above.