Who is this "user" you're talking about? Near every choice in a social media platform design is an engineering choice between conflicting priorities.
The troll who wants to post garbage finds it easier, but the earnest poster now needs to filter out trolls on their own.
The person wanting to co-opt a community label finds it easier, but the person who wants it to continue as-used now has no recourse.
The pervert wanting to upload PG boob-shots definitely finds self-moderation easier, but your change would force rape victims with PTSD to let that smut into their already-curated set of communities.
If you wanted to add a new layer of moderation for posters beneath instance owners and community moderators that might be plausible, but "OP posted something dumb and is getting piled on" is a it's own force your suggestion would abandon.
(And if you think just adding more random part-time moderators to a community would improve its moderation I would encourage to try Improving your next family dinner by giving orders in the kitchen. Especially one that you didn't plan.)
The "State of the Union annual speech" has been pointless since before anyone living was born.
And yet it still happens, because "rapist who breaks all norms" still does it. (Were I a congressional dem, my pick for next speaker would be whomever pledged to not invite an infamous sex pest to ramble in person.)