Outside of a standard set of specific reasons for which it is agreed to be illegal to refuse business (race, sex, orientation etc..), no business is supposed to be able to be compelled -by the government- to associate or transact with another. Instead, boycotts are used by the public themselves (rather than via government strongarming) or by company-to-company action to persuade companies to adjust their behaviour to meet expectations of what is ethically appropriate.
In arrangement, the expectation is not that companies are 'neutral' but that they are sufficiently moderated by public will. This freedom not-to-transact is what allows things such as boycotts of Apartheid South Africa, boycotts of companies that abuse their workers or run sweatshops etc.
There are plenty of ways to rearrange things outside of a Capitalist model, but once you decide to have Capitalism but 'prevent boycotting on political grounds' you're basically suggesting that Capitalism ought to be stripped of one of its extremely few mechanisms for ethical feedback. The implications of that ought to scare you.