I attempted to save a recipe. Because the recipe failed to include the PPG, your site did not allow me to save it. Since your site is so particular about complete recipes, I will not be joining Brwewer's friend.
I agree that validation errors can be annoying but we keep them to a minimum. Sorry you felt that was a deciding factor.
Our intention is to guide brewers to success, and part of that is accurate and complete record keeping. Specifying an ingredient without the ppg would be like listing a hops addition without specifying a time or amount. To complicate matters more, OG cannot be computed without knowing the ppgs for each grain. Several other stats depend on OG - (ABV, IBU, FG) so it is a critical value for the calculator. So, in this particular case, we felt it was better to require ppg and lovibond for custom grains in the interest of accuracy, vs allowing an incomplete line to be saved on the recipe (which would cause confusion later).
I'd be curious to know which ingredient you were trying to add, so we could find the ppg for you. You could always start a thread in the feature request forum too regarding relaxing this requirement. You never know who else might have feedback or +1 the issue. It is something we could change down the road.