petition against body scanners

There is currently no proof that these body scanners are safe for adults, children or pregnant women.

They are illegal to use on children as they would create "indecent images".

Refuse to be scanned!

As I hear it, you can refuse to go through a body scanner and opt for an old-fashioned pat-down search.
Not that I fly anywhere, but supposing I have to, I will be phoning the airport security management beforehand and telling them I will not use a body scanner on grounds of indecency and they will have to make alternative arrangements, if they feel they need to.
They will. A little assertion works wonders, and it's wonderfully empowering.
I would also be making it patently bleeding obvious that I'm not a 'terrorist'. Such a person would want to be completely inconspicuous.

Would be to simply cover your entire body with a layer of noxious material. The Scanner looks for surface features - such as a square of explosive strapped to the body. By carefully covering the whole body the scanner sees no significant distinguishing features. The scanners are, thus, an expensive waste of time, money and resource. They are engineers toys that solve the problem of next years balance sheet not any problem of terrorism.

This circumvention of the scanner might well be impractical - and we all might hope that it is. The point being made is that the scanner does not offer an absolute and effective solution. They offer the false perception of effectiveness which makes the entire system a good deal more dangerous as, it will be reasoned, "nobody can smuggle X on board". This raises the hazardousness of every flight.

Yes there are considerable, important, ethical grounds for rejection of this idea - but there are also practical limitations to what scanners can achieve. Those limitations are nowhere near the limitations of human ingenuity.

if you are starting a petition opposed to something, does it make much sense to host it on the website of the every organisation that has ordered the introduction of what you are opposed?

on top of that, to be included on the petition, the website must send you a confirmation email, where you click on a link

since they are not sending the confirmation emails doesn't seem likely the petition will allow in many signatories

There are concerns within the thinking few that there are possible side effects from the scanner technology.
See wikipedia=terahertz waves.