Just to clarify, I'm assuming that this discussion is about this assertion:
collusion should be legal at every event in every format.
So, I apologize in advance if I'm interpreting the above more literally than it was intended.
Please correct me if you meant something different;
I'm assuming that you are saying that collusion "should" be legal,
not that it "could hypothetically" be legal,
and that you are referring to "every format",
not just unsanctioned Vintage.
Pointing out why the above assertion is incorrect is a daunting task
because, as I perceive it, the scope and subtlety
of what you have not perceived regarding this topic
is of such a high degree
that it is difficult to communicate it to you without writing a post that is far too long.
As a result, I will attempt to explain what I think may clarify my point
without going into much detail.
As I understand it,
all sanctioned tournaments are run under the DCI guidelines as part of a larger system of tournaments,
the point of such tournaments being
to provide an enjoyable experience for Magic players who like to compete.
The assumption is that Magic players who like to compete
enjoy improving their skills in "actual" Magic
and using such skills to defeat their opponents in game.
Under such assumptions, it is safe to assume that these competitive Magic players take pride in winning a tournament
because it is an accomplishment reserved exclusively for those who have proven their skills to everyone else.
However, if it becomes possible for players to practice collusion and bribe their opponents as a means of winning,
winning a tournament no longer means the winner has proven their skills to everyone else.
This will detract from the overall meaning and value of winning a tournament to competitive players.
Winning a tournament is no longer an accomplishment worth attempting since anyone can now win tournaments through bribery.
This is one reason why maintaining the integrity and transparency of tournament proceedings and results is important.
It protects the value and meaning of winning a tournament as a self-explanatory accomplishment
for those who take pride in proving their skills to everyone else.
This is why I brought up the idea
of maintaining transparency of tournament proceedings and results in a way that accounts for collusion.
If this could be done, it would solve the above problem.
Because it would be clear who colluded and who did not,
the new accomplishment for competitive players could be
to win a tournament "with zero bribes".
Keeping track of the extra variable of bribery would be more inefficient than
the current system, which does not have the extra bribery variable to take into account.
In addition, the legalizing of collusion and the resulting hullabaloo
would take energy from all involved in tournament Magic.
The DCI would have to justify their logic, as such a decision would most certainly be unpopular amongst players,
competitive tournament player expectations would have to change,
and potentially negative side effects could result
from Magic being one of the only pastimes (the only pastime?) that has legalized collusion in official tournament play.
The amount of energy needed to legalize collusion and the resulting hullabaloo
would likely be smaller within the unsanctioned Vintage community.
However, such a change would still take energy from all involved
and result in some form of hullabaloo.
So, why do the extra work of legalizing collusion
just so players can do things like bribe their opponents?
What's the upside?
And, if bribery would be, as you have reasonably suggested, very rare,
why should people go through the trouble of incorporating it as an element of tournament Magic
when it would rarely matter or effect match outcomes after being legalized?
True, collusion still could, hypothetically be legalized,
but because legalizing it would be inefficient and troublesome for the above reasons
I do not think it should be legalized
because I perceive no corresponding gain for the cost.
In addition, I'd just like to point out that discussing the legalization of collusion as a hypothetical
or as something that should be instituted without the presentation of any potential, resulting upside from doing so
is, in my opinion, a big, fat waste of time
save the fact that pointing out this discussion as a big, fat waste of time
may prevent similar big, fat wastes of time from cropping up in the future.