Paring clowns wors much better f there's a significant size difference between the tw when introduced. If you raise two clowns together from juvi stage, then it is very likel that they will fight for dominance when they approach sexual maturity. This can resul in srious injury or even fatalities.
As far as inbreeding goes, most CB clowns are inbred to some degree. Platinums are the result ofbreeding two picassos together, and if you trace backthe lineage of any "strain" of icassos, you will find many related indivduals have been paired. This is selective breeding, no necessarily inbreeding. This is the sameprocess used ove millinea to produce the dozens of different dog breeds available today.
Ethical questions arise more for the hobbyist than for the breeder. Breeders will try any pairing they think will produce interesting and viable offspiring. But without te benefit of their experience, a hobbyist is very likely to choose less than optimal specimens to breed. Whether from the same clutch or not. The real question will come years down the line when/if they do spawn. And that is whether or not you try to raise/sell the offspring. Then you will be confronted with the need to cull many of the juvis. And culling them means killing them. Not everyone has the stomache for that.
But in the simple terms, I personally don't have any ethical issue with selective breeding, but I would prefer to get some bloodline seperation. It's not necessary though.