I'm going to be blunt as usual and you may argue against me since nobody believes in marketing, but regardless, just know that it comes with the best intentions.
The join the forum now message at the end of the videos is not very effective. Outright appeals like that are used mainly in donate now or buy the product now messages, and people immediately associate that with the emotional appeal of a cause or the emotional appeal of something new that will make you happy. It also brings out the idea that you're looking for, want and need new members, so already the ideas that something is needed and expected from you comes up twice, so people will naturally not want to continue out of the fear that you might be right and they have to take time out of their busy schedule (which usually includes watching MSNBC) to do something new. They might also be the type of person that doesn't want to step outside of the norm or doesn't want to be seen as part of any group that might be looked down upon, so the idea of belonging to help JTF rather than even just belonging to JTF to help yourself comes up. You do say it to help the country, but when people hear causes and people needing power, they see it as something for you rather than them.
You shouldn't interrupt when your product sells itself. Say this is the place for real information on Israel, America or the Western world, or even just say we are the real Kahanist movement, or whatever find the top three reasons to join JTF and causes that prove what you want really is allowing members/visitors to do something for their country then use a couple of each or even just find the best one to say why JTF is something that is a movement to be joined, or that they can come here to learn what they need.
I actually saw a JTF movie once and forgot it, I think, and never ended up joining. Right away there was a feeling that even this would be to extreme for me, even though I was completely extreme in the wrong direction, but it didn't seem so from the news' presented perspective. Luckily I ending up joining through a link from a blog, and it has been great. Right away though, when people see the movies they don't get the feeling that it's like the Glen Beck speeches that they can talk about, they either think you're trying to steal them away from whatever group or news site its posted in, or they get worried that it's some group of crazy radicals. The JDL and Kach may have had some extreme individuals in it because it was a movement of action, JTF (I know nothing of Hayamin Haamiti) is more of an ideologlical and strictly political advocacy group that happens to support and is based on a poilitical party in Israel which was made possible, once upon a time, through an American group. You have to present is as something simply to gain their interest, because it's equally good to have them as members as having a bunch of people that visit the page, as they could result in new members. You do want a social movement that can make positive change, but fighting for member to join and do that shows you want power, and encouraging recognition through presenting the benefits of your actions shows that joining the moment will empower the visitor.