As I explained here, the key difference as with the Mt ST Helens example, is that the canyon that was caused on days, created effects caused by catastrophe which scientists would never have predicted could happen such as the laminated strata, and a canyon itself.
Actually, I would.
There are plenty of examples of rapid erosion from waves, rivers and ice. Here is an article about it from the people who know - engineering geologists.
Of some interest is this observation:
"The result of such abrasion varies based the material being eroded. For example, a stream in soft sediments will erode more quickly than a stream through solid rock; the same is true for the erosion of a sandy beach versus that of a rocky coastline."
And soft, unconsolidated sediments (or volcanic ash, etc.) can erode with almost no resistance.
The point I am making is, with long ages and uniformity, ...
You need to stop right here. Your problem is that with
long ages and uniformity there is no problem.
... the arguments are based on witnessed processes in the present, but with catastrophes which cause strange features, if that catastrophe has never been witnessed by anyone, then we can't predict all of it's effects, we can only wait until a similar catastrophe such as the canyon created at Mt St Helens, occurs, ...
What you are really telling us is that YEC actually doesn't know anything about its favorite geological event.
... then we can say, "wow look at these effects, who would have thought it."
Plenty of people.
Your position is a strawman argument.
CONCLUSION: Obviously to say before that canyon was made at St Helens, "these features can't be created quickly", ...
Well, considering that no one ever said that ...
... would have been a type of argued ignorance, because really they just didn't know how a catastrophe could cause those features.
Now you admit that you are arguing from ignorance because nobody knows what such an event would do. You don't know, do you?
So while I agree there are evidences which don't seem to fit all that well with a flood, I think basically it is to argue from ignorance to say it can't happen because we don't know how it could have.
The only people saying this seem to be on your side.
Human beings don't know a lot of things, but things that occur are not predicated on humans understanding those events, logically speaking.
And there are a lot of things that human beings DO know. Why should we ignore those things?
P.s. So bickering over these selective selections, would seem to me to be to take the bait a bit.
Ummm, sure. Avoid anything that might refute your position. Let's just declare all engineering geology off limits for this discussion. That way you can make up whatever you want.