Of course, you've got every right to do with your investment as you would.
But, the point is, this is Social Media. Not a business platform. The money that you earn here is not yours. It originates from the Rewards Pool which is currently owned by Steemit Inc. but is actually a part of the people since it has been created by the collective effort of all users on the platform.
It may be their money but is surely not their investment. What you're getting out of the system is not returns on your investment, but rather rewards from the community based on how people appreciate your words. Self-upvoting is a method of cheating around that system by looking to drain the rewards pool, which includes taking rewards for others for your own personal gain. STEEM isn't being grown on trees here. There is a limited amount of it remaining on the platform, and the only way to replenish it is to interact more and bring in new people to the platform.
The rewards pool is there because of the people. The rewards pool is there for the people. The rewards are gained by those who are worthy of it as deemed by all on Steemit. The rewards pool is not for people looking to make money and treating this platform as an investment.