I think this is a valid topic, and I'm surprised your former church faulted you for it.
1) If Jesus told us that unless we become like little children we would not enter the kingdom of God, why do so many christians choose to view movies that the world says are not suitable for children under the age of 17?
I was under the impression that this referred to adults maintaining the unquestioning faith of children, not behaving childishly in all things. It needs to be taken into account that adults differ from children in many ways, including emotional maturity (hopefully). Thus, an adult would probably be more capable then a child of understanding the reason for the addition of violence or sex into a film and could, unlike young kids and teens, consciously reject the message to conform to the values presented onscreen.
That said, everyone, not just Christians, should think carefully about their entertainment choices. It's important to look at the reason for the labels, not just the ratings themselves. As mentioned, the film "The Passion" was given an R rating because of it's graphic depiction of violence and brutality against Christ - but many Christian parents and churches took busloads of Sunday schoolers and kids from youth groups to go see it. At the same time, lots of parents did not want their kid to see "Harry Potter and the Prisoner of Azkaban", which had a lighter rating. They made a choice based on content, not just labelling. My parents let me see "Born on the Fourth of July" as a juvenille despite it's rating, but freaked that I was into "River's Edge" which had the same rating but far different content.
Is watching a romantic comedy with casual premarital sex in it a good way to tell the world that we (Christians) do not approve of premarital sex?
No, I suppose not, but there are also times which someone exposes themselves to something they do not approve of for the purposes of learning. I couldn't justify it for a romantic comedy or something without any lessons or information (PWP), but take "Alexander", with it's homosexual themes, for example. My mom, a Christian, watched it with me, gay kisses and all, because of the information and historical content. She wasn't watching it as a turn on or because she wanted to see Jared Leto make out with a guy (I think) but because it gave her some basic info on Alexander and she is just now getting into Greek and Roman history. She wouldn't watch something like "American Pie" with it's sex references, but overlooked the sexual themes in the "Alexander" film because of what it was about.
Is viewing violence and gore harmless to a christians mind?
Viewing violence and gore is not harmless to anyone's mind, Christians included, but again I think it is logical to look at the purpose of the violence. Is it there to make a point, like in "The Passion", or is it gratuitous, like "Jason vs Freddy"? Does it have a point? In "Saving Private Ryan" and "Black Hawk Down" violence is necessary to make the point...whereas in "Terminator" which is fictional it's just to set the scene. Evaluating the pros and cons of each film you decide to watch is probably useful - does the point of the movie and the lessons taught justify the violence (or other objectionable content)?
Do you remember when we were children; when violence, gore, sex and profanity used to be nightmarishly disturbing and wrong? What made us change our minds along the way?
A lot of it still
is disturbing to me - I cringed and cried during "The Passion" even thought I understood why it was bloody, I get sick feeling when I watch slasher films and I blush during sexual references (especially while watching "Alexander" with my mother!). I don't enjoy watching movies where casual sex is the norm unless I understand the film is trying to convey the personality of a particular character and has a good reason for doing so - I wouldn't watch something like "Sex in the City" because that's just not what I'm into. Swearing does not bother me when I understand the point - again, to communicate the personality of a character or to reflect someone's views - but it annoys me when it's used excessively and purposelessly just because it has shock value.