Power corrupts anything. It doesn't matter whether it started out with good intentions or as an alternative to another corrupt power. The more power, the more corruption. And monopolies are very powerful thus very corrupted.
We must not only tolerate, but celebrate and promote economic, cultural and political diversity and alternatives.
Let me tell it again.
On top of economic monopolies, there could also be politic monopolies and cultural monopolies.
Same as with economic monopolies, we should avoid politic and cultural monopolies.
We do need political and cultural diversity.