I'd say that finding women attractive is quite normal and healthy for men.
From my personal experience, the part where it turns into One-Itis (which I'd like to assume the definition to be unhealthy and obsessive thoughts and actions with the intent of getting one chick to "fall for you") is when we: take some sort of action (ask her out...try to micro-flirt, etc) -> don't get the result we want (rejection, her being repulsed, etc) -> and then doubling down that there's some "glimmer of hope" with this chick, causing you to keep trying. Rinse and repeat the same process over and over again with the same chick, with new "techniques" all while sacrificing the integral areas of your manhood.
Once we actually get that bit of rejection, our brains trick us to overvalue that which we are attempting to obtain. That's why sometimess, we get one-itis for chicks who aren't even all that, and we look back at those one-itis moments and absolutely cringe and feel embarassed for ourselves.
So. Find a chick hot. Are you going to take action? If yes, do so (generally speaking, attempt to get her on a date or on some kind of alone time). If she rejects you the first time, forget about her and move on asap. On to the NEXT. That's how you stop the one-itis from budding.
Basically, any negative results = MOVE ON. Anything other than that will result in one-itis forming.