this would be the wrong move, for 3 reasons:

1) Not enough service time. Also, he played most of his career with Montreal, and his number is retired by the successor Nationals.
2) This would open up a pandora’s box, which would also result in retiring the numbers of Keith Hernandez (17), Darryl Strawberry (18), Edgardo Alfonzo (13), Dwight Gooden (16) and Jerry Koosman (36). We are not the Yankees. (Though to be fair, their retired numbers were done so thoughtfully.)
3) His stats over the span are far too comparable to several other players over a span of a similar length of time. (Carlos Beltran is one example.) Even though Carter manned a championship pitching staff behind the plate for 4+ years, there isn’t enough of a convincing argument for his number to be retired.

Lastly, though not exactly a 4th reason, we’re letting the emotional state of affairs override our better judgment if we do this. At the very least, he’s in the Mets’ Hall of Fame