Is it permissible to eat McDonalds / Pizza Hut and so on?
If the place is obviously not a halal place you should avoid it because at these places they will sell pork and there can be a chance that this comes into contact with vegetarian products.
Don’t worry about the people. We look at the statements and actions of people of knowledge and not the people.
What is the effect of eating haraam?
- One’s du’a is not accepted.
- One’s emaan weakens as we will say that it’s fine as we are not eating pork even though it is being cooked in the same kitchen. Then one will be weak in another important area of Islam and so on.
As for places like McDonalds etc a person would need to verify that the oils are not mixing, even utensils. If they are, it would make the food haraam not by being haraam in and of itself but due to an external factor.
A persons Islam is reflected in different ways. For example, if a person is lax in something as major as what they are eating then they will be lax in something else. It also causes desensitisation to things.