It's nothing against left or even right politics. It's just the reality check that in every nation, it's largely the swing vote which determines if you win or lose. Win first, discuss policy details later. Common sense and realpolitik is that you need to win the swing. The faithful largely take care of themselves. Having an extended shitfight to ensure you have as idealogically "pure" a candidate as possible is the worst sort of thing to do. It's the proverbial "preaching to the choir". "firing up the base" is inward looking. You need to expand your base, and you can't expand jack shit without listening to what language other people use. If you just shout louder with the same language you've always used, how can you expect to win over anyone who's not already convinced? You need to tailor your message to appeal to more people, not just berate everyone else for not "getting it".
You can discuss details all you like if you are the losers but it won't help.
EDIT: If you "fire up the base" you're going to see results like getting 60% instead of 55% in places like California, which due to the current constitutional rules, doesn't count for anything. Maybe the system sucks, but that's the system you need to master in order to win. Maybe it should be by popular vote, sure, but right now, it isn't, so barring an upset that overturns the electoral college, this is the reality of how things work. get into state politics if you want a better chance of overturning the EC.