The Pelosi-governed House Rules deleted the a provision of the prior House Rules that provided in essence a percentage of the members of a committee "...shall be appointed on the recommendation of the Minority Leader."
Pelosi was allowed to do as she pleased in that regard, and she intentionally picked anti-Trumpers.
Her alteration of the Rules was a total power grab and the R's in the House should have loudly protested at length. That they did not is a tell of many sorts.
What is your argument the "Committee is illegal"?
The rules and the power of the use of committee was not followed.
Pelosi thinks she is GOD. He knows she is not.