Do we really need testers? or Don't do everything by youself

Recently we have had a conversation with colleagues about "Do we really need testers?" Why should we have someone dedicated to this role? Can't I do testing, documenting by myself or with a  help of another developer to get a different point of view? Code review and automation would be done faster by developers. They know product, architecture, they're experienced in development, unit testing, automation. And end-to-end testing could be done with a whole team including product owners and managers. So, why do we need them?

Of course we as engineers can do everything, but one person should not do everything! Developer or tester should be exited about what he/she is doing and it's very rare case when developers like to test thoroughly and waste their time writing test plans, thinking about test strategies, assuming customer point of view, spending time on a long discussions and so on. We are already doing a log of different tasks in today's software development era especially those engineers who are working withing DevOps model. I't not every time possible to do everything with the highest quality and that's basically why we should split our roles at some point. Testers becoming more technical, they're developing automation frameworks, supporting environments, deploying, maintaining and more responsibilities are coming all the time. Not only test plans, reporting and manual testing anymore. And are you still really want to do everything and more by yourself?