Sure, but not everyone's opinion is equally valid. I've worked with a number of design teams who confuse their opinion (an educated opinion, which I respect) as a fact. Facts beat opinions -- if a short-term optimization will be a long term loser, then prove it.
Unfortunately, it's not really possible to prove/disprove an opinion on what a design element will do.
Additionally, optimization testing allows you to try out different options. Going with someone's (educated) gut feel is a worse decision than exploring the option space.
Ideally, you'd test everything. In the real world, resource constraints apply, so at issue is how to establish an internal discipline where facts trump opinions, and opinions can be tested then either discarded or confirmed.