Before my time, but I have a keen interest in 1960s football and I believe pitch invasions first became an issue when kids started running onto the pitch when their team scored a goal around 1961ish, TV commentator Ken Wolstenholme called it out as a stupid new trend, I think it was at Millwall of all places but probably TV had a lot to do with it, either with people seeing it as an opportunity to get themselves seen on television (a big deal in those days) or TV facilitating a copy cat phenomena. A bit of both probably.

Saturday 2nd December 1967, another televised match (London region) Fulham v Liverpool, a spectator runs onto the pitch and strikes a player, Jimmy Conroy. By the mid 1970s, following the "legitimised" violence, disruption and destruction of 1968 with police brutality as well police being attacked, we've got segregation coming in - that is to say sections being fenced off at the sides rather than perimeter fences - and we've got reports of fans then charging across parts of the pitch to leap into and get involved in fights in other stands.

So we then go to perimeter fences with more and more police, which only helps create a more menacing atmosphere and we climax with 97 dead in one single incident, all of whom would have walked out of that ground alive had those fences not been there.

So where are we going with this?
If we're saying we have to allow people on the pitch to celebrate or protest, then you're going to get everything that goes with it.
If not, what do we do to stop it?

I really don't know. Perhaps we should just play politics with it and blame the other side.