Bill,

It seems you need to do some good apologetic studying. Why don't you start with the book Catholicism and Fundamentalism: The Attack on "Romanism" by "Bible Christians"
by Karl Keating. You could get it online at any Catholic site that carries books. Go check out Catholicity.com for many links or Catholic Answers.

As far as Seventh Day Adventism goes, you have the same problem, as with all of Protestantism:

They provide their own set of rules as is convenient to them. In other words, while they claim they alone use the Bible authentically as the sole authority, they act very inconsistently.

For example, ask your friend where he gets the list of what books belong in the Bible.

• How does he know what the inspired Word of God is?
  Make sure you know the in's and out's of the Canon arguments.
• Ask him where the Bible says that you may only have one wife?

There are many issues that these Protestants solve by tradition, just as Catholics do, that are no where in Scripture.

The difference is that Catholics believe Jesus gave us the Church, the true Catholic Church, the authority to teach in His Name and create norms for worship, therefore Catholics admit to the validity and authority of tradition; we know what tradition is: authoritative. The Church gave us the true teaching on the canon of Scripture, the sacraments (i.e. Marriage against [polygamy, like some Mormons], etc.) and everything else.

Study up! There are no shortcuts to good apologetics. In the end, the most effective witness is holiness and consistency.

• Practice what you preach, and
• act charitably

That will speak volumes about where the truth lies.

Peace and good luck,

Bob K.