(Yes, I know "socialism" and "capitalism" are vague terms, hence why you should probably very much clarify what type of "socialist" system you want, since "socialism" can be anything from market socialism, Marxism-Leninism, Syndicalism, democratic socialism, Trotskyism, anarcho-socialism, anarcho-communism, Luxemburgism, etc. Also, I'm a far cry from informed in this, so please correct me when needed.)

So anyway, if you call yourself a socialist or at least want to abolish capitalism, why?

So for the best reasons I have seen are:

• Capitalism is inherently hierarchical and incompatible with democracy, which is egalitarian.

Obviously not all types of socialism (I.E, most types of socialism that have been tried for more than a few years because they weren't overthrown or voted out) are egalitarian however and many of these systems are completely centralized.

• Big companies will naturally use the state to their own advantage, as capitalism is driven by self interest instead of any vague marker of "competition".

The main argument against this is that you definitely regulate capitalism to be more competitive with stuff like antitrust without abolishing the whole thing.