I have come across examples where views make it easier to introduce performance problems. Especially when columns are an outcome of a function or case statement etc. A view might be a good instrument to collect combined data that is often accessed but it hides the physical structure of the tables.

Recently I tuned a query that got data from view with a filter on a column that was actually an outcome of a calculation. Rewriting using only the tables got it speedy.

So I would say views are a good instrument in the hands of experts and require proper disclaimers for usage.