It depends what you're working on. If you've got a project that has to grow fast, adding more features than fixing bugs, not even knowing what you're going to keep in a few months, the time spent fixing regression bugs due to lack of tests I think is relatively little.

You may say "I'll thank myself later", but in this sort of business there won't be a later if we're not fast enough. It's a lesser of evils thing.

It would be nice if testing were a faster thing to do. The faster you can do it, the lower the threshold would be for this sort of a judgement call.