Year in year out, up and down the country, fans run on the pitch to celebrate success - be that winning the Premiership or avoiding relegation from League 2. I'm puzzled as to why you find it so terrible and why you think some of our fans shouldn't do it. The players and manager were able to walk around the pitch afterwards anyway.
For the record, I did not run on the pitch on Monday - I'm past that sort of thing - but I recall doing it at Darlington as a teenager, to celebrate the 4th Division title, along with several thousand others. Still a great memory all these years later.