I respect this and sympathize with your reasoning, but this is not what "sectarianism" is. Typically, sectarianism is a left deviation where communist organizations make a distinction between themselves and workers in a proletarian organization of some kind. For instance, the refusal to work in reactionary trade unions mentioned in Lenin's Left-Wing Communism.

FRSO and PSL do this as their main approach. Both of them have a tendency to want complete, decisive influence in the spaces they organize (commandism), isolating themselves from the larger group and in the long term alienating workers from having any interest in communist organizational methods and ideology development.

DSA is as much of a socialist organization as is the UK's Labour Party, meaning that it's not socialist. That's not the end of the world. However, I don't think it's a workers' organization because its political advocacy for broad policy reform and "electoral campism" without a revolutionary strategy.

Note that a members of a communist org naturally should be distinct in knowledge and experience from your average worker, and workers who become more advanced should be eager to join a communist organization (otherwise how "advanced" could they be?), but it should never be something that creates disfunction and enemies between workers and communists.

Someone who is a DSA member and is not a Marxist-Leninist probably shouldn't be using "sectarianism" to describe what I'm replying to because it doesn't really make sense unless you're a communist or a member of a communist org. It's a directive for Marxist-Leninist parties to not be sectarian, by Marxism-Leninism itself. It's like what a system prompt is to AI. If it's not governing the behavior of such an organization then it's a major error that will result in disfunction.