You have to judge it client by client though. Some are amenable to and grateful for a flatly stated analysis and recommendation, even if it goes against their ideas. Some will feel belittled and undermined. You need both sorts to pay their invoices and refer their peers, so you pick your battles.
> Some will feel belittled and undermined.
This has always frustrated me. You wouldn't go to a doctor, hear that you need an appendix removed, and feel "belittled and undermined"!
The 'problem' (it's a problem from my pov) is that clients simply think they know better when it comes to digital/computer/online stuff. They're used to browsing the web, so they think they know what a good website is. They know how to write a letter in MS Word, so they think they can write good web copy. Etc.