Dr. Soon may even truly believe his science is valid, but the funding he receives creates a lopsided megaphone which unfairly skews the perception of the debate.
Having a conflict of interest is understandable; hiding a conflict of interest is problematic.
By the same token, all scientists who receive funding from the pharmaceutical industry or groups they influence, should be barred from publishing papers on vaccine safety.
Scientists who receive funding from, for example, the pharmaceutical industry are expected to fully and explicitly disclose potentially conflicting interests--and by golly, they do. It's taken quite seriously, actually. If you look at any article in a respectable medical journal today, you'll find a section of the manuscript that's explicitly headed with Conflicting interests: or something synonymous. It will appear on every article, even on the ones where it's followed by "None declared" or the like, just so that it's clear that the journal asked for and got an on-the-record response from the article's authors. It doesn't remove the potential bias associated with outside funding, but it at least makes the potential for bias transparent.
Lying about competing interests - even through omission - is looked on very poorly by serious, credible medical researchers. Interestingly, one of the many, many types of misconduct engaged in by Andrew Wakefield was his failure to disclose significant financial interests when he published his (now-retracted and thoroughly discredited) Lancet paper suggesting a link between the MMR vaccine and autism. (Wakefield wasn't receiving pharmaceutical money, of course; he collected almost half a million pounds from lawyers involved in an anti-MMR lawsuit.)
And while the practice of mandatory disclosure started with the medical journals, the expectation has gradually bled across into other fields as well, particularly among top-tier journals.