In Fact, a Continued Attack on Public Education
The purpose of 529 is squarely in line with the GOP's continued promotion of private schools to replace the public school system. The tax deferral feature of 529 has the effect of placing part of the tax burden for private school subsidies on the general taxpaying population. (That includes, by the way, private schools that rely primarily on religious organizations.)
The GOP has been at war with free public education since its inception back in the 19th century. They'll never let up. They're committed. Education should be the province of the "elite" against they themselves rail... when it seems to get votes.