I put in volunteer time helping with handing out information and educating the public (as well as collecting petition signatures / mail your mp letters... fat lot of good that did). This is an accurate description of what I experienced when talking with people in the street. People start off dismissive but once they learn about the problems with the bill, the vast majority would say they were opposed.
Meanwhile the government has been spewing fear mongering propaganda since the Bill came out
Or, they reasonably calculate that the risk/reward is in their favor? Even if the law is used 100% to suppress political dissent, it's not like the government is going to target people expressing mainstream conservative viewpoints.
What they usually hear is "this bill will stop terrorism - well, that's good enough for me!" and don't research the issue any further.
Most people would especially be furious to learn that such bills don't in fact stop terrorism and they are just lied to so the governments gets more power. But because they don't have a good understanding of the issue themselves they just think that's just some "liberal propaganda trying to remove our small government (ironically) guys from power", or whatever.