Footballers are not known for their sportsmanship but this is one occasion when there is an unwritten code which most players understand and abide by. However, I agree with Boz that it was a legitimate goal which the referee had to allow. What should have happened is that the Guiseley manager should have ordered his team to let Braintree have a walk-in goal.
I remember a few years ago, Kanu scored a similar goal for Arsenal in the FA Cup against Sheffield United. He was unaware of the unwritten rule. Arsene Wenger to his credit asked the FA to have the game replayed. Surprisingly, they agreed and the result was the same!
I don't see that happening this time. Guiseley have said it was regrettable but have not yet said anything should be done about it. In any case, it would mean an extra fixture for Braintree, which they may actually lose.
No doubt for the rest of the season NL fans will be telling the Guiseley team what they think about the incident - including the SWA in a few days. They should all be seriously embarrassed.