If you want to edit porn then you will need video editing software that can handle the content that you want to edit. Forget about trying to get porn using free software. There is no point in wasting time with iMovie or Windows movie maker.
Those programs are great for home video or to learn the very basic of editing, but in the end they will leave you frustrated and begging for more options.
If you going to be a serious porn video editor, then the only was to go is to take yourself seriously and get the editing software that will continuously update and grow with you. For this reason, I would recommend . Yeah sure, the initial price tag can look a little too much, but for that price you get access to updates as soon as Adobe release them.
Premiere Pro is what I would call "industry standard". Which to me means that if you can master Premiere Pro then you can easily work for other production companies if you have Premiere Pro on your editing CV.
Another good reason for using Premiere Pro is that there is a ton of free tutorial, hint and tip available on YouTube. there are many Premiere Pro "Guru's" that you can search for to find professional advice.
I have edited porn videos using Final Cut Pro for 4 years, but 6 months ago I made the switch to Premiere Pro and wish I did it years ago. Premiere Pro just feels more stable and fluid that FCP ever did.
You can even tweet me if you want anymore information regarding porn video editing.