Forced tithing is no different from forced circumcision. I'm not against encouraging people to commit to giving 10% of their increase as a way to become a covenant partner in ministry. But to dangle them over Hell if they don't is bringing them under bondage to the Law. A pledge or vow to give so much or to give 10% is very important. And breaking a vow or pledge is just as much "sin" as not tithing was under the Law.
Deuteronomy 23:21 (ESV)
“If you make a vow to the Lord your God, you shall not delay fulfilling it, for the Lord your God will surely require it of you, and you will be guilty of sin."
The point is... we should give as we have determined in our hearts. And we should commit to supporting the ministry as financial partners. And yes, we are responsible to God for our commitments. We can fail God and the work of God by not fulfilling our vows or commitments as it relates to the body.
Giving is still a very serious matter, even under grace.