I have reviewed dozens of healthcare Mutual Funds and ETF's and compared them to the major indexes (mostly S&P), as far as back in the 1980's. It appears that the healthcare sector has always outperformed the general market by quite a lot, being in the double digits in annual returns most of the time . It even appears to have less losses than the general market during market crashes. Knowing that in the U.S there is little chance of major political disruption on healthcare, why isn't this sector a "must" on every investor's portfolio? Am I missing something?
It is a must in most folks' portfolios. If you invest in S&P 500 ETFs/funds, you'll have a decent amount of healthcare. If you invest in actively managed value, blend, and growth mutual funds, you'll also get healthcare. If you're rolling your own portfolio (in the US), you might consider starting with a general purpose health company (e.g. J&J), then maybe add a large pharma company (e.g. Pfizer, Merck, etc), then top off with some more specialized/focused companies.
Of course, you don't want to put all of your portfolio in healthcare alone. There are other sectors that also have good long-term outlooks (energy & tech, as well).
EDIT: Added link to Morningstar portfolio analysis for SPX.
The fact that you have thought of this means that many others have too, which has increased its price to a fair level, accordingly. You may want to read a bit about the Efficient Market Hypothesis.