There are many passages and quotable concepts in the Course which could be used to back up either viewpoint.
I think though the main reason people struggle with this is because the EGO has tremendous difficulty understanding anything outside of its backwards perspective.
For example, to the ego, control brings you freedom. It says that if you control things more, you'll be able to prevent all the things you don't want to happen, and enforce all the things you do want to happen. You'll 'get your way', and that means life will seem to be doing what you want it to do. And that is its interpretation of what freedom is.
The truth, which the ego cannot grasp or accept, is that control DIMINISHES your freedom, because it separates out some parts (of yourself ultimately) from others, sets them against each other, and elects to support only one of the two parts. Now your choices are diminished. In other words, if you choose A or B, once you've chosen, the other choice goes away, and now you are 'stuck' with the choice you made. This is freedom to the ego, but to your Real Self this is imprisonment.
So when you use the ego mind to try to understand a very basic principle like ACCEPTANCE, this I think is where the community's viewpoint hinges and stimulates controversy. It's because the ego does not understand HOW it could be possible that you can be accepting, or just working on changing how you perceive the world, and not be passive. So this is what it all pivots around.
Really these are the two conflicting attitudes of the EGO:
1) Accept everything as it is, don't try to change anything, be passive, work on your own mind, change your mind ABOUT the world, study in secret, don't tell anyone you're doing the Course, keep miracles to yourself, interpret miracles as shifts in your own perception only, and generally lay down any kind of 'interference' with the world as you go within. This is EGO because the ego has now separated you from the world, has isolated you to your body/mind with the justification of hundreds of Course quotes which SEEM to support its argument. This is EGO because the ego can't ALLOW there to be acceptance without interpreting it as SACRIFICE, i.e. the giving up of control which the ego thinks means like 'I need do nothing' i.e. I will literally stop expressing anything in the world. This is SPIRITUAL CONSTIPATION! You'll be stuck in your head and paralyzed from exerting the will and power of God. You will be disabled. The ego sees acceptance as disempowerment and disability, and this inspires all thoughts of how this kind of 'attitude' is the correct way to do the Course.
2) The second ego interpretation is that you aren't meant to just dwell on fixing your view of the world, but you're meant to change the world. Except that, to the ego, this means, using the ego to change the world. This turns into control. It turns into spiritualization of the world. It becomes the ego's party where all egos are invited to 'act spiritual' or to pursue special causes or use your ACIM learning to 'attack' what is. The EGO can't understand whatsoever how it could be possible to express something in the world and have it be ACCEPTING of the world at the same time. It does not get this. So if you were to express or exert or change the world, this is now considered 'unacceptable' to the Course theology, and therefore rejected by many students. And yet those who accept this idea then go on to shy away from some of the seemingly contradictory statements about acceptance or doing God's will or changing your mind and so on. This again is another ego play to flip your mind around a polarity of DUALITY, so that you stay within the ego thought system, and keep interpreting the course WITH the ego.
Neither of these camps have the truth.
Truth is of the Holy Spirit and his mind functions in a completely different way with rules that apply to all and which has no duality in it. The Holy Spirit has a completely different understanding of ACCEPTANCE. He has a completely different grasp of whether you are 'for or against' doing stuff in the world, knowing that this is a dualistic question. Holy Spirit would not see your 'accepting things as they are' attitude as being SEPARATE from 'being empowered to do God's will and heal the world'. And therefore, Holy Spirit supports BOTH camps combined, which completely defies the ego's logic.
It is possible to be accepting without that having to mean, you cut yourself off from the world or disappear into your intellectual correction of perception. It is possible to be accepting of what 'is' or what appears to be happening, while at the same time having the power and will to CHANGE IT. Because... after all, IT is just an effect of what's going on in the mind. IT is a dream that YOU are dreaming. So this has to mean, you can accept what you have made, but you can also make something different. So this division of separation in the community is really only there because the EGO has gotten ahold of the Course and DOES NOT understand the Holy Spirit's viewpoint or thought system.
As always with ANY polarizing, dualistic, separating set of questions, in which it seems that neither side seems to 'get it', this ALWAYS means that "there has to be a better way" and there always IS a third option. It's that third option that comes from Holy Spirit. Another way not just of looking at the situation, but another way of looking at HOW you look at looking at the situation.
You can accept without being controlling, and yet exercise tremendous freedom to intercede. "I [Jesus] inspire all miracles, which are really intercessions. They intercede for your holiness." - principle 32. "35 - Miracles are expressions of love, but they may not always have observable effects." - principle 35, which also means miracles USUALLY have observable effects, meaning they change the world.
There is not a contradiction here. The contradiction is in the ego mind that cannot understand this. It can't get it because the ego can only see WITH separation. It is blind to Oneness or true meaning. Any separation in the community has to be founded in the ego.