"I'm working on such an app now, and right now the fastest way I can get anything done is writing similar code to what I wrote in 2003. It's not quite as bad, but I continually succumb to doubt."

The biggest objective problem this style has is that it affords everything-injection; cross-site scripting attacks, SQL injection, command injection if you're using shell commands, etc. Every time you bash one string together with another one, you run the serious risk of introducing a security attack, and with this style of programming, you basically have to be thinking about every single string concatenation.

Using a framework that will take some of the cognitive load off can be a net gain. It need not be a Glorious Framework, it just needs to be something that makes doing the right thing easier than doing the wrong thing.

Otherwise, most of the rest of the pain will be felt by you, not your customers, so hey, whatever, go nuts. But this is a legitimate objection to this approach. (And a legitimate objection to every framework that fails to make the right thing easier than the wrong thing, which is still a great deal of them.)