By well-meaning baby leftist I assume you are talking about situations where you have a good-faith conversation with somebody who doesn't dismiss you as an authoritarian extremist red-fash tankie out of hand and you're not in an online pissing contest with shitlibs.

People arrive at the well-meaning soft left because they see all the things that are wrong with the world and feel a moral outrage against poverty, climate disaster, bigotry and all the rest. They see the problems and reject the current state of the world but they're still stuck in the liberal way of conceptualising politics; ie. you make a convincing argument in the marketplace of ideas (preferably using humour and politeness), you protest peacefully and then when you have convinced enough people they will vote for someone who will finally do the nice and sensible things and that is you step outside of the bounds of acceptable political action, unspecified bad stuff will happen.

Your job as the baby leftist's radical friend is to demonstrate the futility of that liberal notion of politics but to do so in an empathetic way. Talking about the history of stuff like Operation Gladio, the coup against Allende or cointelpro can be a powerful way of sowing distrust, so can discussions about corporate media, the role of money in politics, broken promises from "progressive" liberal politicians or said politicians' impotence against the far right. You should be the doomer, showing how liberals have always failed "progressive" causes and how they're currently failing them and making the case that they will continue to fail.

Once the baby leftist is beginning to question the system as opposed to just specific policies you call talk about political action that has made social progress possible. How people won rights and improved their lives by bypassing the bureaucratic trap of bourgeois parliamentarianism. People went on strike, they fought cops, they beat up Nazis, they broke rules and they were rude and impolite to their oppressors. Somewhere people even made fully-fledged revolutions that didn't only banish illiteracy, sexism and exploitation from these places but also scared the bourgeoisie globally into making concessions.

The important thing in all of this is to be empathetic and listening. Nobody wants to be lectured or talked down to. There's also good reasons why baby leftists are still stuck in the liberal mind prison, the most obvious being that it is what they have been indoctrinated into believing all their lives and they get confirmation from the media and the people around them that they're right. It takes more than a single discussion with some guy to change that. Also, voting on things after having had a rational good-faith debate enlightened by objective facts is not a bad way to make decisions and you shouldn't be dismissing it out of hand. The problem is not that votes and debates doesn't work as such but rather that capitalist class society makes such things impossible to realise as anything but empty theatre.