Why are monopolies bad?

If they have a monopoly there is no similar product. You PAY.

Lack of competition, fewer options for consumers, more expensive.

If there's a monopoly, there aren't other options for people to buy it somewhere else.

Because the consumer will have a smaller consumer surplus while the producer can maximize his profits still. The price will be set at mc=mr which is higher than mc or the price in the perfectly competitive market.

You literally answered your own question. The point of stopping market monopoly is so that consumers have choice. You ended by saying people will shop for a similar product. But if a company monopolizes a market, from where would they find a similar product? That's the point, variety and choice for the consumer. This, in theory, drives growth and development of new businesses. If they have a chance. That's what anti-monopoly laws are supposed to protect. 

You just said why; it allows a company to raise the price and hold the consumer hostage because in a monopoly there IS NO similar product available. A monopoly means the company owns and controls all the desirable versions of any product or service.