Notice how the entire Chapter of Romans 14 does not make sense unless we acknowledge that our faith, though nurtured by God, is nonetheless to a huge degree a matter of personal opinion. How we make sense of this journey we are on is never more than a personal opinion. It is good enough for God that while on the path of the Gospel where we abide in Jesus that we at least have an opinion. This is about being on the journey and abiding in Christ, not about demanding that my understanding of that path is technically more correct to that of others.
This brings up the question, what does it mean to stumble? Do we cause a person to stumble simply because we have an opinion they disagree with or dislike or find uncomfortable? Didn't Paul who wrote Romans 14 also say many things others disagreed with, or disliked or found uncomfortable? I think that when we teach things or insist on things or argue for things that cause people to abandon the journey, that is when we cause them to stumble. I think the idea is that so long as someone abides in Christ, so long as they remain engaged, then they are headed to a destination that NONE OF US has yet reached. It simply makes no sense to engage another in such a way that it knocks them off that path.
Sure some opinions are indeed better than others, but when it comes to righteousness, peace and joy -- well then it really makes little difference whose personal opinion is technically better.
One thing is for sure, personal opinions are only useful to the person who holds them. They can possess some use value when shared for others to consider. But when used as a shibboleth to create an US who are by definition accepted by God and a THEM rejected by God then it goes too far.
But can we take the message from Romans 14 too far? Didn't Paul rebuke Peter for distancing himself from gentiles when the Jews showed up? Didn't Paul rail against those trying to bring law back into the church at Galatia? It seems that the ONLY stumbling blocks Paul is concerned about are those we use to clutter the pathway where someone is already abiding in Jesus. However, when people create alternate routes that deny the simplicity of the gospel or cause them to stray from the path, Paul sought to absolutely clutter that alternate path with objections intended to make them abandon that alternate pathway.
The way I have made sense of Romans 14, however has the prerequisite of recognizing that all understanding, even the understanding we have of Jesus is personal opinion. Peter confessed to Jesus, "You are the Christ the Son of the Living God!" Peter knew this to be true by revelation, but Peter's behavior afterwards demonstrates that although Peter knew it to be true, he clearly misunderstood what it means to apply that truth or how that truth changes everything. The confidence we have in Jesus, or in the bible, or in the reality that Christ abides with us, is not based on how we conceptually understand and justify that confidence but rather in how that confidence inarticulately resonates as so true deep in our hearts. Do not do that which sabotages a brother's or sister's experience of that deep down inside resonating confidence in the unconditional love of God being communicated as they abide in Jesus.
I would also see a danger in misapplying the teaching of Romans 14 as a way of that allows us to control those whose behavior and expressed opinions complicate sectarian subcultural opinions. It is not a message to shut up and keep your differences of opinion to yourself.
But lastly Romans 14 leaves me feeling that those who think their faith is more than just a personal opinion ARE often the very ones placing a huge stumbling blocks in the path. Those who are convinced that their opinion was given to them directly by God, those who believe that their understanding was given to them by revelation from the Holy Spirit and is therefore THE CORRECT BIBLICAL TEACHING and no longer a mere personal opinion, these are those who seek out a greater control of the traffic patterns on this path to God than is necessary and in doing so unwittingly push many off the path where they had begun to abide in Jesus.