We boat in some really pristine waters in Northern Ontario and I support efforts to move to cleaner burning 4-stroke motors. (Electric motors would be great, but we are totally off the grid, so I’m not sure how that would work.)
We have both an older (1974?) Johnson 2-stroke 9.9 and a new Mercury 9.9 4-stroke. The Mercury is heavier, harder to start (warm or cold) and is a little less zippy than the Johnson. Maybe our Merc is a lemon, but in our case, (at least for smaller outboards), it seems like there is something of a trade off for the cleaner four-stroke versus the simple, but dirtier two-stroke.