If you read through my whole post you'll see that we're in agreement, I think!
Well at least with the first part of your post, the second part I think you're wrong, tries have been disallowed when no defenders been obstructed.

The act of crossing on its own is IMO not sufficient to draw a penalty, distance and more importantly impediment have to be taken into account

They are! Like I said, obstruction is never given when the crossing occurs way down field, it's only ever given in close quarters when an attacker is placed between ball carrier and defender.

It's a joke because it only comes into play on televised matches. Quite simple really. It it was scrutinised as heavily in every single match then it wouldn't be as much of a problem. Not hard to understand that

Yet we've seen tries disallowed when the sweep runner is way in front of the impeded defender who has no chance of getting to him. So even in some close quarter events the distance can be mitigating yet the try gets chalked off anyway.

The clue you gave yourself but failed to notice is "IMPEDED" defender. If you impede a defender then (barring an advantage being played) you concede a penalty. Whether he would have made the tackle is irrelevant, it is not just that immediate particular tackle, it is a deliberate and offside disruption of the defence. The penalty will also be given regardless of whether a try follows. It would be the same coming away from his own line.

It is the job of the dummy runner not to impede or obstruct the defence and it is up to the ball carrier not to run behind his own man,

Except that wasn't the rule for obstruction which needed a would be tackler to be obstructed. Nobody owns the space, players can be wherever they want, you just can't move to block a would be tackler.

Danny McGuire at MM last year against Wigan, he ran behind a man nowhere near the defensive line, no-one was impeded in anyway, there was no obstruction in the sense someone was obstructed.

NOW I'll join the obstruction criticism bandwagon.

Since when was obstruction multidirectional? Surely if a defender rushes out the line, as Huddersfield just did, and end up in the attacking line, they cannot claim to be obstructed by the attacking players who are stood [uto the side[/i of them?!

Pathetic rule. Garbage defence being let off by stupid "obstruction" calls.

Yes but that was against Wigan.

We all know the 11th commandment - Thou shalt not give a 50/50 video ref decision against wigan.

Translation: Wiggin had a try decision go against them.

You forgot the bylaw whereby invisible knock ons can be given against them though.