I understand what you're saying, but this is an issue that mostly exists between (don't like this term much but can't think of a better one) extremely terminally-online leftists who do not organize.
Going offline, this is generally just not an issue, the orgs filled with people who just argue over theory also don't do much and shouldn't be listened to. It's a large movement and there are bound to be people who are unfortunately less effective.
I didn't bother discussing how online leftist infighting affects real life, it's not relevant compared to, say, the much realer issue of left-orgs blowing up because of, say, someone being outed as a sex pest or someone slandering someone they don't like anymore (which isn't an issue only relegated to the left, the right does this way more often)