So let's say, you decide to create your own programming language, now you can automatically afford to do as much work as the organizations behind mainstream programming languages? Organizations with thousands of contributors, funding, etc.?
Now, let's omit that for a moment. Let's say that after having implemented your language after years of work, now for some reason you got 1 prospect user.
That person will ask you about: syntax highlighting, linting, code navigation, testing, packaging, documentation, operating systems/architecture support, etc. Who is going to contribute all that if you are busy writing everything by hand?
Unless you have as much time as Terry Davis, you are better off starting by piggybacking on something that exists. Then, once you have an idea that scales, you can convince other people to help you and have a successful project. Then you can have a viable ecosystem that people can comfortably join.
The real problem about parsing is not parsing the formal grammar. It's deciding what to store about the parsed input (CST to AST) and designing the ancillary datastructures for further processing, integrating the parser with the rest of the application, etc.
The real problem about building a compiler is everything else but not parsing. Parsing is the easiest part. Once you've written a view recursive descent parsers you will probably agree.
The parser for syntax highlighting is probably a different one than the parser for AST generation and compilation. So is a parser for batch compilation different to one for incremental compilation. Even the syntax might be different.
Using YACC doesn't give you magical integration with IDEs, operating systems, testing, documentation and so on. I feel as if you took my specific comment about parsers (which are not hard to write at all, few hundred lines of code for a moderately complex language) in an inappropriately general way as in "don't use anything for anything when doing anything".
That's agreeable. We seems to disagree on how to achieve that ideal - on the specific point of whether to use a parser generator or not. The correct answer is not :)
Now, let's omit that for a moment. Let's say that after having implemented your language after years of work, now for some reason you got 1 prospect user.
That person will ask you about: syntax highlighting, linting, code navigation, testing, packaging, documentation, operating systems/architecture support, etc. Who is going to contribute all that if you are busy writing everything by hand?
Unless you have as much time as Terry Davis, you are better off starting by piggybacking on something that exists. Then, once you have an idea that scales, you can convince other people to help you and have a successful project. Then you can have a viable ecosystem that people can comfortably join.