Because Calvin were in complete agreement /Sarc
http://lexloiz.wordpress.com/2009/01/15/john-calvin-and-martin-luther-%E2%80%93-some-differences/
http://confessionalouthouse.wordpress.com/2014/04/28/luther-vs-calvin-on-images/
Let's not forget about that whole predestination vs. self determination thing either. And how about that Faith alone?
Lets not leave out ole Zwingli either:
Luther- the bread and the wine are really the Body and the Blood of Jesus Christ, given for the remission of sins.
Calvin- Christ is spiritually present in the bread and the wind.
Zwingli- the bread and the wine are only symbolic and consumed as a memorial for Jesus Christ.
Who is it that doesn't understand Sola Scriptura?
All your points are well taken. I think what they mean by Sola Scriptura is not that they interpret the Scriptures correctly, or even consistently, but that it is theoretically possible. This definition: "Sola scriptura (Latin ablative, "by Scripture alone") is the doctrine that the Bible contains all knowledge necessary for salvation and holiness" says nothing about rightly interpreting the Scripture. OTOH, one could end up with thousands of new heresies, denomination, sects, cults, and even religions as well from those trying to apply Sola Scriptura to their personal relationship or reforms.
Mostly its the RC folk who seem not to understand Sola Scriptura. We have had to sit here and listen to many misrepresentations. I am sure most of these are based on the lack of a studied understanding and not malicious. But erroneous nonetheless.
BTW, arguments from diversity of belief are largely irrelevant. We do not argue divine theology on consequentialist grounds. What is true is true regardless of how well or poorly we fallen sinners have interacted with it.
Nevertheless, given the choices you presented, I would take any of them over transubstatiation, which has no grounding in Scripture or reason, but tends rather to encourage idolatry. It is one of the principal reasons I could never become Catholic, even if I betrayed everything else the Lord has taught me from His word. By the grace of God, I will never give my adoration to a bloodless wafer that has no power to save. My prayer is that He would help me remain true to Him until the end of my days (not too long from now). So with His help, I will bend my knee to no created thing ever, but only to Him, in spirit and in truth.