There's a few different issues here and they're becoming conflated.
Saturday had nothing to do with fans sitting in the wrong seats. It was more than over zealous handling and the culprits here were the stewards.
That said, on other match days, I'm not sure what the best answer is. We always try and arrive early enough to grab our own actual seats and sit together, but I do sympathise with groups who can't buy together wanting to sit together, however they often don't only want to be together which they could often easily achieve on the outer edges, but they want to be together in the congested middle with the best view and disregard for anyone else. That I do take exception to.
What should happen is that all away ends are unreserved seats, then there is no argument, it's simply first come first serve and fair for everyone, but until we get that, then sit where you're allocated.
At least when it is unreserved and the steward wants you to move, you can ask - ok show me where is free and I'll go there. It did seem on Saturday like it was oversold, but I'm sure that won't be the case due to H&S if anything bad had happened, I don't think the club would risk it.