Suppose you have a rule that anything your group does needs 100 % perfect consensus. This can work in a very small group (like six people), it can also work in a slightly larger group (ten to twenty) if people know each other well. If your rule is pure consensus, then one single saboteur can block anything. If you want to make it easy to join, how is that supposed to work out? The downfall doesn't require infiltration, it can be just an attention-seeker. And if you want to use pure consensus in a group of a thousand people, failure doesn't need any bad person, it simply doesn't work at that scale.
Consensus decision-making is a very late development in lefty/anarchist movements, it comes from the US peace movement and they had received that from the practice of some Quakers (religious people living together with all sorts of rituals how they talk with each other). Now, some folks come up with ideas how to patch things, like consensus minus one or consensus minus two. Suppose a group with such a rule set grows. What then happens is that it gets harder and harder to reach the threshold for making any decision. If you want bigger agreement than simple majorities, it makes more sense to fix a percentage like 70 %. But why would you want something more than the normal majority threshold to begin with? If the default is doing nothing, super majorities just make it more likely that you don't decide to do anything. If you believe the current state of affairs is awesome, then it makes sense to have super majorities for everything.
The real issue is the gap between wishing for something and actually making it a reality. There is no point in having 90 % or even a 100 % voting that they want X to happen if they are all together to weak to make it happen. And if 51 % want something to happen, and they are enough to make it happen without help form the other 49 %, that's good enough. The decision rule should be majoritarian in that a minority is not allowed to actively undermine a majority (calling a decision stupid after it is made doesn't count as undermining though), and consensus-oriented in that a person who voted against doing X is not ordered to do anything for it.
If your group meets in person and you have enough space, and you aren't all super-introverted, you can decide by wish/do compass: The moderator asks people to position themselves on a line based on how much they want X to happen, and ask them then to also position themselves on another axis based on how much they want to do for that thing. The moderator then walks to people and asks them about why they chose their position (not everybody needs to be asked for every question, the extreme positions are more important and the moderator should also keep track of people who haven't said much yet).
For issuing statements bearing the group's name, super majorities can make sense. The question here is do you even want to come across as a monolithic entity? If you are okay with having ongoing discussion published, with different opinion pieces marked as such, why should these need majority approval? So, for issuing statements, there can be two tiers: 1. official position of the group (requiring something like 80 % approval threshold), 2. opinion piece (like 20 % to prevent trolls). People can vote publish, publish with opinion disclaimer, not publish. If the threshold for the first option isn't reached, these votes automatically count towards the second threshold.