I have workd for myself and as an employee, and I don't think it's true that the self-employed pay extra taxes. The only reason it looks like that is because of the SE tax, but that basically offsets employer contributions for payroll employees (ie it's money that doesn't look like it's coming out of an employee's paycheck, but really it is part of the difference between what an employer has to pay, and what the employee gets).
I think the issue is that you have more control over how you spend that money. Anything that could be a dual purpose - conference at a resort for instance - goes in as a business expense and does not get taxed. It is an inducement to overconsume if you can book the expense as a business expense.
I agree those incentives exist.
I've been responsible for the finances of a Subchapter S corp. owned by a small circle of individuals. Sure, business expenses are pre-tax, which means, depending on your bracket, you save roughly a third versus post-tax expenses. But they're still expenses, and any good business person strives to minimize unnecessary expenses. I've never seen an instance in which we spent money simply because it was "deductible."