The problem with SELinux
Has nothing to do with trust, since a) it's open source and thus fully auditable, and b) the NSA washed their hands of it years ago (indeed they regret ever having released it, which is a very good sign), and thus no longer have any influence over it (and it's not like there's any obscure encryption code in there that could have been deliberately weakened).
No, the problem with SELinux is it's just too damned complicated for the average user to understand and maintain, which itself represents a security risk, because if you can't understand it then you can't use it effectively, in fact you're literally lulled into a false sense of security. You end up completely dependent on upstream and/or distro maintainers to provide secure SELinux policies (so in that sense I suppose it really is a question of trust), and sadly they are not only fallible but indeed sometimes appear to have a rather contemptuous attitude toward security.
See PolicyKit as another equally complex and obfuscated example.
I'm a firm believer in the KISS principle, or as da Vinci once put it; "Simplicity is the ultimate sophistication". The complexity of SELinux makes it utterly useless, IMO, and quite possibly dangerous.