First, people do have visions/prophecies today, and they are accepted by others when God speaks to them. It says in 1 Corinthians 14:1 ‘Follow the way of love and eagerly desire spiritual gifts, especially the gift of prophecy’. Christians are also told not to treat prophecies with contempt, and to ‘Test everything. Hold on to the good. Avoid every kind of evil.’ (1 Thessalonians 5:20-21)
Second, Jesus wasn’t exactly accepted when he spoke the word of God. Hence his execution. He was only widely accepted when he rose from the dead – see the book of Acts for how the situation turned from 11hopeless men to thousands upon thousands being converted across the world.