There are reasons for not posting a script on a public site. The most obvious is that the idea can be stolen. While it may stimulate a writer to take an idea in a new direction, most writers would not simply lift the idea as his/her own. However, posting short excerpts for critique is reasonable. Often the first 10 pages or a problem section is sufficient.
Another reason is that I may be hired to revise or develop a script for which I do not own the rights or have signed an NDA so I can't legally share or disclose content publicly.
Also, I may have co-authored a work and I don't have my co-author's permission.
Or, a script is completed but has been submitted for consideration. Scripts that are in submission are often tricky. A few production companies and/or contests will not accept public manuscripts to minimize liability issues. Ironically, that's why some contest winning scripts are not picked up for production. A built-in safeguard for some competitions is that the participating producers have the right of first option.
HOWEVER, most writers are only looking for feedback on shorts, rough drafts and/or non-commercial scripts which they will produce themselves. This forum is ideally aimed for those writers or with specific questions. And there are some members of the forum who will read the full scripts privately and provide feedback. It isn't intended to replace services which provide detailed feedback on a feature script. I know a couple premier members offer discounts for their services to IndieTalk members wanting a more comprehensive review.
There are pros and cons for posting here. Pros first. If you're a new scriptwriter, posting the first ten pages or a short excerpt can be helpful in giving feedback. That short segment would not compromise the integrity of the rest of your script. In fact, that's pretty much the amount a professional reader will read before making the call of passing on or considering your script. You can get good feedback on story, structure and formatting. The con is that not everyone who comments has the same level of experience. I won't lie, not all advice is sound and not all feedback is kind. We're all human and have our pet peeves. The reality is to survive in the entertainment industry, you need a thick skin. If you only expect praise, posting is probably not a good idea on any public forum.
I have to say, that I find IndieTalk a very supportive community overall with some very talented and knowledgeable people in the independent film business. It's a good place to learn if used properly. Those seeking others to write their scripts for them or provide free script reviews will be disappointed. If you are sincere about wanting to improve, you'll find a great deal of support.