I’ve refrained from posting on the voucher debate for a variety of reasons. But I realized some of my comments on other blogs were longer than some of my posts here.
The following comes with the hopefully unnecessary caveat that the opinions stated here are my own, and may not be representative of any group or government body I may be affiliated with.
The nature of groups
It is the nature of groups to villainize some amorphous group or ideal and simultaneously deify their own position. Groups gain validity and cohesion by identifying enemies.  It’s one of the central themes of Orwell’s 1984 that an irreconcilable conflict is essential to influencing group behavior.
In the Slashdot community, condemnation Microsoft is almost expected, as is praise of Apple or Linux. At sporting events, fans form an unofficial group. At first the “enemy” is the opposing team. This focus can shift quickly to a particular person such as a dirty player, or referee. At first, the shouts of disdain come from a single source, and left unchecked, spread to an increasing number of fans. 
Whether it’s technologists’ rants against Microsoft, a sports fan blaming the referee, or the increasing partisianship in national politics, groupthink is a potent force if there is an identifiable enemy.
There is something personally validating about being part of a group. It’s encouraging to know others think as we do. We feel more important when we identify with a group.
As a result of self-indentifying with groups, defensive behavior is common. An attack on our group is somehow personal. Left unchecked, the group’s arguments stray from logic and principles and become overly broad, emotional, and fallacious as members rationalize and defend their association. (I think we can all point fingers at someone else who has skipped the first step and jumped straight to unfounded vitriol.)
How does this apply to the voucher debate? If you’ve made it this far, it’s a fair bet you have the intellectual perspicacity to figure it out on your own. I’ll highlight a few points anyway.
I’ve said before that most of the PCE radio ads offend me, particularly the ones they were running at the beginning of the year. The ads offended for several reasons: the ads depicted overly broad generalizations poorly disguised as metaphors while simultaneously vilifying public education. It’s okay to lobby for more choices (I might even agree with you!), but if you try to tell me a parent has no options in the public system, you lose credibility.
The Utah Taxpayers Association has done a good bit of research into the fiscal impact of voucher programs, and regularly cites well-known authorities like the Friedman Foundation and the Cato Institute. Their recent post crossed the line from factual advocacy to the emotional groupthink behavior I described above. The post smacks a bit of ad hominem. In other words, I hear them making the following argument in their post: this other group (but not us) will behave poorly, so clearly we’re right, and their wrong.
The UTA post also lumps together moderates and extremists. They predict a series of actions if the referendum fails. They miss two key points: a) the farther down the list one goes, I suspect the number of people supporting the action decreasing, until only those on the wings are left, and b) the list applies to both sides of the issue.
To be fair, voucher opponents like Utahns For Public Schools have (more subtly) inserted their own variation of ad hominem, believing that perhaps discrediting the source cripples the argument. You’ve heard the rationale: The voucher movement is being funded primarily by out-of-state interests (as part of a national experiment/conspiracy), ergo, vouchers aren’t good for Utah.
What to do?
We live a country where reasonable people have disagreed since before its founding. Even our bicameral national congress is a form of compromise. If we recognize the dangers (and inherence) of group mentality, it is easier to keep discussion useful and productive.