I do not agree with this position. Yes, liberal democracy is a system to domesticate the people as their participation is limited to casting votes every X years. Yes, many working class parties that engage in liberal politics end up being corrupted by the system. However, abstaining from elections only made the leftist radical discourse and ability to influence policy outcomes almost null.
Note that this is the opposite tendency of what is happening right now in Asia, with Leninist parties in Sri Lanka, India (Kerala), Nepal and others disputing and winning elections. And let's not forget the recent experiences of Venezuela, which carried out a revolution, and Colombia, with the first leftist president in the last century, which is being able to push reforms with all the other powers (legislative, judicial) against it. Or even the Bolivian case, which was able to push many reforms against the system and even overcome a bourgeois coup and a lawfare campaign.
If the radical party is able to push a popular agenda by pitting the people against the Congress, they will damage the moral of these institutions that claim to represent the will of the people, but in fact represent the interests of the capitalists. We need to destroy the system from all sides.
The big mistake is thinking that winning elections is an end in itself. Any political move must seek economic and organizational gains. The left must seek power over the bourgeois state and ability to mobilize the masses and not simply winning elections and becoming managers of bourgeois interests.