Pashuteh Yid:
Sure, one can have kashos. I have lot’s of kashon on lots of sugyos. I have had kashon on sugyos in hilchos shabbos, on kashrus, on all sorts of things.
Having kashos doesn’t make you a rasha. Deciding based on your kashos that you will therefore stop observing the halachos you have kashos on- that makes you a rasha.
It is also extremely arrogant. To think that after thousands of years, you finally found the kasha that has no answer, is just ridiculous. Especially if you happen to be an am haaretz.