It's unclear if that's still true or not. The most recent good data is a Gallup poll from 2006.[1] When asked if the constitution should be amended (the only way such a ban could exist), support was at 54%. Also, support was higher in the 90's. If trends have continued, supporters should be in the minority today.

Also, it's a bit rich to compare a nonexistent flag burning ban (which would punish with fines or jail) to Pakistan's very-much-existent blasphemy laws (which execute people).

1. http://www.gallup.com/poll/23524/public-support-constitution...