Nice, thoughtful response. Thank you.
I would argue that the religious leaders of Jesus' day thought that their traditions were sacred, too. The test is whether they nullify Scripture. Protestants (well, many of us) would argue that things like purgatory, praying to saints, and the various Marian beliefs do contradict Scriptures, at least at times. I can take you to Catholic churches in Dallas that I love and consider to be firmly based in the Scriptures, but I can also take you to Catholic churches (especially Hispanic) that I believe would shock you with their practices.
The proper term is "invocation" of saints. I understand where you're coming from - but I believe a Scriptural argument can be made for purgatory, invocation and the specific Marian dogmas of the immaculate conception and the assumption. All those doctrines tie in with the larger Catholic theology of the Scriptures.
I can take you to Catholic churches in Dallas that I love and consider to be firmly based in the Scriptures, but I can also take you to Catholic churches (especially Hispanic) that I believe would shock you with their practices.
I'm certain that you could. Of course, by the same token, I'm sure there are Protestant churches that would scandalize you with their crassness or their superstition. Even Rastafarians claim to be a Bible-only Reformed religion.
The Catechism of the Catholic Church is the best guide for finding out about the doctrines we really believe, and the General Instruction on the Roman Missal is the best guide for finding out what liturgical rites we really follow.
And that gets to the heart of the ol "Authority Debate". Who is given the authority to infallibly interpret the Holy Scriptures? Everybody will of course say God, and that is obviously correct. But how? Not only is there disagreements between the Catholic Church and various Protestant denominations on correct interpretation, the various Protestant Churches and ecclesial communions have conflicting interpretations between each other as well.
I would argue that Protestants, while not calling it by this name, also depend on tradition to interpret the Bible as well. They have too! Just look at all the comments concerning Scripture in this thread alone. Put 10 people alone in a room to read the Bible for the first time, and you've just given birth to 10 new denominations. Your average lay person has to rely on some authority to help guide them in understanding the Bible. Problem is, where does the tradition come from?
...but I can also take you to Catholic churches (especially Hispanic) that I believe would shock you with their practices.
Bet you can't! :-) I speak of being shocked.
But again, I would wager that you are seeing what we affectionately refer to as the "small t" traditions or customs, as opposed to "Capital T" Sacred Tradition. The two are different, but often get confused. And yes, these can become wrong real quickly. Hence our Lord founding His Church on the 12 Apostles with St. Peter as their head to authoritatively guide and protect the Church into all Truth, and protect against incorrect human traditions. Human traditions (take Church Law for example) do come into play and have to (we're human). The just need to be correlated correctly to the Word of God - hence the Church's claim of authority.