Why did the red pills in Morpheus's crew even enter the Matrix in the first place in the first movie?
Was it for Neo to see the Oracle?
Other than that, I don't see any point in entering the Matrix. What do the red pills gain from entering the Matrix?
I only watched the first movie and this is bugging me.
They entered the Matrix a few times in the first movie, each for a slightly different reason.
The basic answer, in all cases, is that red pills can only interact with people that are plugged into the Matrix if they are also connected. This is also the only way they can interact with the programs that exist in the Matrix. So, the times they entered The Matrix in the first movie:
Soon after that, they went back in to take Neo to see The Oracle. The only way they knew to meet her was at her apartment, inside the Matrix, and Neo had to go there.
(I'm not clear on whether or not, by that point, they knew that she was actually another program.)
At the climax, they went in to get Morpheus. Since he was taken hostage while plugged in, they couldn't unplug him until his consciousness could reach a exit, so they needed to go back in, take on the programs holding him, and get him out.
Other than going in to find Neo, the primary reason they plug back into the Matrix is to find more humans to unplug. As @Richard points out, while they are connected, they will commit acts of hacking, which are designed to draw the same kind of people that are likely to accept their "sales pitch". I assume they also spend some of their time inside scouting for intel and performing minor acts of domestic terrorism.
(I also get the impression, mostly from the second and third movies, that it's only a small number of people that routinely go back into the Matrix, and based on the behavior of people like Lock, that no everyone agrees they should be doing it so frequently, but that's just my opinion.)
I don't think the question was worded well, since I don't think the crew were ever referred to as "red pills". I think Cypher referred to people within the Matrix as different pill colors (red/blue) to describe those that were oblivious and wanted to stay that way, and those that would want to know, and could accept, the truth, if it was presented to them. To answer, we'd need to decide if we are talking about "red pills" as in, the consciousnesses of the crew, or the pills themselves.
If asking about why the "red pills", themselves, entered the Matrix and why they exist, they are programs set up to hack the Matrix and allow a person to be found and freed - probably written by Trinity or other human hackers. That's why after Neo takes the pill, you see Trinity and the crew working to locate Neo and unlock the "battery cell" Neo is in - we can infer that the pill has something to do with that process during that scene. When Neo wakes up after his acupuncture to restore his muscles, he asks about the pill and they confirm for him that the pill was a program used to find and free him.
As far as why the crew went into the Matrix - more than just to free the enslaved and, my guess, for intelligence gathering on what the machines might be doing - was, at least in the first movie, to:
