English Translation
Many people rely on the television to form their own opinion.
意見を「もつ」is not common. It should be 持つ in Kanji.
「意見を持つのにテレビに頼っている」sounds like an unnatural word-for-word translation. 「多くの人々」instead of「多くの人」is redundant. I would propose:
テレビが世論形成に及ぼす影響は大きい。（テレビがよろんけいせいにおよぼすえいきょうはおおきい）
I intentionally swapped the subject and the object because starting from TV as a subject sounds more natural in Japanese.
Please google yourself with the key phrase “テレビ” + “世論形成”. You’ll find many articles about this topic.