Both of them as Marx defined them are incompatible with other ideas and so deserve slurs. There are progressive ideologies with influence from Marx that do allow for other ideas to exist. There are many people who will throw away all of liberal philosophy for pure socialism. As soon as you allow for the liberal differences in outcome you have to agree for there won't be true socialism and you have to debate what (if any!) level of safety net you provide and further accept there should not be agreement. This isn't just that we won't agree, but the strong statement that an agreement would be a bad thing.
Why should one care how Marx defined "socialism"? The term predates him by many decades, so he doesn't get to say what is "true socialism" and what isn't.
And with that you showed exactly why I have the knee jerk reaction to attack communism every time it is brought up. There is a constant play of this type of thing and people are starting to think that because it is unchallenged it might be right.
Those 'progressive ideologies' with influence from Marx are what make all of what we see today happen. From killing people if they cant pay for healthcare to these sociopathic layoffs 'because AI'. So 'influence from Marx' is just nonsense.
The simple reason why other ideas are not compatible with those two are because those 'other ideas' are geared for making this happen to maximize profit of the few. That's why they are incompatible and whenever you allow them this is what you end up with.
Both of them as Marx defined them are incompatible with other ideas and so deserve slurs. There are progressive ideologies with influence from Marx that do allow for other ideas to exist. There are many people who will throw away all of liberal philosophy for pure socialism. As soon as you allow for the liberal differences in outcome you have to agree for there won't be true socialism and you have to debate what (if any!) level of safety net you provide and further accept there should not be agreement. This isn't just that we won't agree, but the strong statement that an agreement would be a bad thing.