I initially agreed with you, but am now concerned that changing other people's values in this way is inherently immoral mind-hijacking. Yes, in one sense you are just giving them more information. But the effect would not be the same if the information was merely listed, rather than accompanied by shocking videos, so it is not just information. Additionally, they've previously presumably decided not to look into the matter further,* in which case you are intervening in their mental family to undermine system 2 and support system 1. Certainly if people showed me such videos without my informed consent I would consider it hostile action.
*(if they had they were evidently unswayed by the videos and you will achieve less through repeated exposure than you might from someone who had never seen them before)
But the effect would not be the same if the information was merely listed, rather than accompanied by shocking videos
The effect would not be the same if there was less information, rather than more. The extra imagery adds additional information.
Assuming that the technology and videos had been available, would you have considered it immoral to show the citizens of Nazi Germany videos from concentration camps? People who might have decided to not look further into the issue of Jewish treatment within their country?
I notice that a large fraction of Effective Altruism people are vegetarian. This makes sense: in general Effective Altruists take moral issues seriously, even when that means changing your lifestyle. I'm not sure it's a good balance, though.
One way to think about this is to convert it into money. How much would I need to be paid to give up eating meat? All animal products? How much money would I need to spend on myself to be about as happy as I would be with less money but continuing to eat animals? I'd probably be willing to go vegetarian for about $500/year, vegan for maybe $2000/year.
It turns out you can probably pay to convince other people to be vegetarian much more cheaply than that. I estimate the cost of a vegetarian-year at $4.29 to $536 while Brian Tomasik estimates $11 with better methodology (which I looked at). This is by placing ads on facebook for a site where people can watch an animial cruelty video and ideally become vegetarian or vegan.
If you would get more than $11/year worth of enjoyment out of continuing to eat meat, why not give $11/year to convince someone else to not eat meat for you? Or give $50/year and be on the safe side?
(While you're giving money, you should probably give it to the organization that you think will do the most good with it, which I think is probably one of GiveWell's top charities. The nice thing about money as opposed to actions is that it's easy to redirect.)
I also posted this on my blog.