Is It Ever OK to Tell Lies about Road Safety?

So it's well established by now that some people on uk.rec.cycling say
things about road safety that they know (or at least suspect) aren't
really true, the "reasoning" behind that approach being that telling
those lies leads to us having measures that encourage cycling and/or
discourage motoring, and doing that saves so many lives that its worth
lying, even if that lie costs some (but fewer) lives in itself.

Prominent examples of this include:

- Cycle helmets: "If I tell lies about helmets and pretend that they
don't save lives, and convince others of this through my lies, then it
is less likely that helmets will become compulsory. Not having the
inconvenience of helmet compulsion will encourage more people to cycle
(and therefore fewer people to drive), and this will save far more lives
than the helmets themselves would. Therefore pretending that helmets
don't save lives when they do is beneficial to society."

- Speed cameras: "If I tell lies about cameras and pretend that they
save lives when they don't (and they probably actually kill people), and
convince others of this through my lies, then it is more likely that we
will have more cameras. The more cameras we have, the more people will
stop driving (and maybe start cycling instead), because cameras
(together with very low speed limits) make things so unpleasant for
motorists. This modal shift will save more lives than those that are
lost by having the cameras. Therefore pretending that cameras save
lives when they arguably cost lives (and at the very least are
frequently used instead of genuine life-saving measures) is beneficial
to society."

The question is, is it OK to lie about road safety if you genuinely
believe that doing so will have a net benefit to society in the way
described? I firmly believe that it isn't, but clearly some people
think it is, otherwise they wouldn't do it. I don't think people should
be "playing God" like this, deciding who gets to live and who dies.
Would the family of someone killed by not having a helmet (having
swallowed the anti-helmet propaganda) be OK with being told "It's all
right, his death is in a good cause as 1.8 other people who would have
died will now not die due to the lies we've told your son"?

And anyway, where do these people get their figures from? The truth is
that they can't be anywhere near 100% sure just how many lives (if any)
would really be saved by modal shift from cars to bicycles...any
conclusions are going to be highly speculative at best. I don't think
people should be telling lies about a life-and-death subject like road
safety when they don't even have any proper proof that those lies really
will do any good whatsoever. I think there's a lot of wishful thinking
involved he these people want everyone out of their cars and on their
bikes for all sorts of "reasons", and I think the "modal shift would
save x lives a year" thing is just tacked on in an attempt to justify
telling lies which will result in deaths.

Telling lies about road safety is not OK, and those who continually do
it (we all know who they are by now) ought to hang their heads in shame.
It is incompatible with being a responsible, decent member of society,
which I'm sure a lot of these people see themselves as. If they do then
they really should stop kidding themselves that propagating lies about
something so important is in any way acceptable. It's time it stopped
please.