Learn Spanish (Spain): Creo que tu postura es muy polémica. - I think that your stance is very controversial.

In Spanish, affirmative phrases expressing belief, like creo que (I think that), are followed by the indicative mood because you are stating what you consider to be a fact. You only use the subjunctive if you make the phrase negative, like no creo que sea (I don't think it is), which introduces doubt.

Does postura only refer to someone's physical posture?

No. While postura can mean physical posture, it is widely used to mean a person's stance, position, or attitude regarding a specific topic or debate, just like in this sentence.

Is polémica a false friend for the English word polemic?

Partially, yes. While an English polemic is usually a noun meaning a strong verbal attack, polémico or polémica is extremely common in Spanish as an adjective meaning controversial. So, muy polémica translates naturally to very controversial.

Why is there no written accent on tu?

The word tu without a written accent is the possessive adjective meaning your, which we see here in tu postura. You only use the accent mark on tú when it is the subject pronoun meaning you.