Rome said very clearly and specifically that it is not always a sin to attend the SSPX. The quote has been posted here about 10 times. You have quoted from the document yourself.
Going to the SSPX is only a sin if one goes for sinful reasons. Hence, it is not always a sin. This does not mean that it is sometimes ok to sin; it means that sometimes the action of going to the SSPX is a sin, and sometimes it is not.
It is a sin to miss Mass. But it is not a sin to miss Mass if you’re sick. This does not mean that it’s ok to sin when you’re sick; it means that the action itself is only sometimes sinful.
What are you trying to get at by comparing the SSPX to masturbation, contraception, murderers, Old Catholics, etc
The Ecclesia Dei Commission, created by Pope John Paul II, didn’t say “you can have a lessened degree of guilt for the sin of going to the SSPX.” It said, “you commit no sin by going to the SSPX for devotion the traditional Mass.”
Do you not agree with Jimmy Akin that using illicit matter for the consecration renders the celebration illicit?
catholic.com/thisrock/1999/9905chap.asp
Nobody said anything about invalid Masses. That’s totally different from illicit. The SSPX never celebrate invalid Masses.
Everyone is aware that the Commission discourages going to the SSPX, as I pointed that out several times in my original posts. The Commission also said that it is not necessarily a sin to go, and that you may fulfill your Sunday obligation by going there, and that you may donate money to them.
You ignore the parts of the Ecclesia Dei letters that you don’t like as “personal opinions”, but you quote other parts of the very same letters as authoritative

It just doesn’t make sense.
More irrelevance…whether Rome discourages attendance of the SSPX has nothing to do with whether it a sin to disobey their suggestion. Rome makes lots of suggestions that we aren’t morally bound to follow.
You’re using the word “illegal” for dramatic effect. Why not just say “illicit”, which is the correct term.
I explained in my original posts on the subject that the Commission discourages attending the Masses. I also explained that it is not a sin to choose to attend anyway.
I can only explain the same thing so many times-- they discourage attending the SSPX, but that does not make it a sin. They said specifically that it is not a sin. It is you who picks and chooses which parts of the Commission’s teachings you want to accept.
Honestly, it seems like you’re just trying to change the subject to avoid talking about your original claims that it is a sin to attend illicit/SSPX Masses. Are you ever going to quote the law or church document that prohibits Catholics from attending illicit Masses?