Once again, we see the scribes miss the message.
The scribes see what is going on at a party. Here is Jesus, sitting with tax collectors and sinners. How did they see this? The scribes were not invited to the party. They were looking in to see the things that Jesus was doing. They were interested in His life, but were surprised to see a Man of righteousness sharing time with people that were not righteous (at least in the scribe's eyes).
Jesus tells them the answer to the question in their hearts: Verse 17 says, "It is not those who are healthy that need a physician, but those who are sick." We often stop reading there, but this is not all that Jesus has to say on the subject.
To look at that sentence, we realize that Jesus is talking about His target audience.
Now, look at the last part of the sentence: "I did not come to call the righteous, but sinners."
Jesus is speaking about more than just His target audience. He is talking about His mission.
Jesus has done more in Mark 2 than just reach out to a sinner or tax collector - He CALLS a tax collector.
Are you reaching out to people that are lost in sin - or are you calling them to a better way of life? After an encounter with you, where does the sinner want to be? In sin or in Christ? Who is the healthy? Who is the sick?