You wouldn't be turning your base into a plantation (i think a limit as to how many flower pots one could have is a decent idea, maybe 3 pots maximum) and they certainly aren't forced to, the concept of expression is subjective to each individual (i say this being an artist myself) if you don't want berries in your base because of whatever reason you may have, then plant them outside and not on your base, and if it annoys you to see berries in other people's bases, don't forget it's their base and that is up to them to decide whether or not to have them there, it's almost as if i liked rock music and disliked hip-hop but still went ahead and listened to it just to then complain about how i think hip-hop is garbage, you made a valid point but we can't really talk objectively about something that is subjective by itself such as expression. Maybe comparing a secret base to an art museum is a bit odd since well, it's more like a personal hideout room, in a museum there's stuff made by many different people, and the museum itself is not directly bound to the things that are on display nor does it have any influence on the artists that produced them, while one's room/hideout/base has a bit of the owner's personality rather than someone else's and it does actively influence someone, prompting them to want to change something in the room for something else, of course not everyone will be pleased by the way the room is arranged, while they might be pleased after some things have been moved or changed because again, expression reflects one's personality, not that of others.