I should think that the non-tithers need to MYOB, eh?
I can't speak for anyone else, but for myself I will say this: it's a doctrinal issue, no less than the deity of Christ or the necessity of baptism. If I see my brothers and sisters believing and doing something which is not aligned with the whole counsel of Scripture, should I remain silent?
For years I paid a tenth of my income to my local church, under the belief that it was the biblically-sound thing to do. Then I started to question it, because the alleged blessings (Malachi 3) simply weren't appearing. I did a lot of reading, looked up every single reference in scripture and read many books and articles on the subject. I spent many weeks looking into it, and found that, without exception, every article or book in support of tithing violated one or more principles of sound hermeneutics. Not that the non-tithing articles were exempt, but many were sound.
I came to the conclusion that tithing is part of the Old Covenant. Yes, it is
mentioned before Moses, in Genesis 14 and 28. However, it is not
commanded before Moses, whereas circumcision is. Galatians explains clearly that circumcision is not necessary, so the argument that tithing is still necessary (because it was mentioned before Moses) is absolutely groundless. Some have said that tithing was never abrogated... well neither was stoning homosexuals and persistently wayward children, but as Christians we don't do those things. Read Acts 15:1-35.
Many people conflate 'giving' with 'tithing', or think that people who don't tithe, don't give at all. Both are incorrect! Mostly, the people who are against tithing are against the legalistic interpretation which says Christians are under some scriptural obligation to tithe. I've read many such arguments in this thread. I can show Scripture to refute them, but only the Holy Spirit can impart the truth to our hearts.
Dear brothers and sisters in Christ, we are free from the Law. It has been fulfilled completely in Christ. Let's not put ourselves under that yoke again, for if we think that we must tithe to gain, earn, or maintain God's favour, we have fallen from grace. If we must tithe, then we must uphold the entire Law... read Galatians 5:3-4.
Should we give from our income? Yes! Should we support the local church and Christian ministries? Yes! Should we give generously, and even sacrificially at times? Yes! But none of these equate to tithing; they simply are not the same thing!
We can discuss all day of what the OT tithe(s) actually consisted, or how many times it is mentioned in the NT, or what the storehouse is, but frankly those are red herrings.
Rather, let me invite all those who still believe that tithing is
required to read Galatians (and Romans, Hebrews, and particularly Acts 15) carefully. If you think you can refute the Jerusalem Council and Paul's arguments and defend your belief, I welcome you to try. I also suggest that you accept the amazing grace of God as offered to us in Jesus Christ, who has set us free from the Law.