Porn actresses can only give consent by contract, but a contract does not constitute meaningful consent. A meaningful consent is such that it can be withdrawn anytime, including during a sex act.
Of course. Porn actresses have the right to withdraw their consent at any point, as much as any other worker has the right to walk out on their job (assuming that doing so won’t endanger other people—airline pilot shouldn’t be allowed to parachute out of a plane during a flight, for example).
Perhaps what you are trying to say is that workers’ rights are not always fully respected in porn, but that problem is hardly unique to the sex industry. We need feminist, labor, and other social justice movements to focus on challenging abuses of workers’ rights within porn or in any other industries, rather than treating porn actresses as inherently having no rights.
A porn actress has to follow instructions given by directors.
That’s what workers do in any capitalist workplace: workers follow instructions given by their bosses. This supervisorial authority can be abused, which once again leads to why we need social movements and labor rights protections. Porn may be a unique work environment, but abuses of workers’ rights that take place there are similar to any other workplace, especially those that are considered low-status.
There is no way a consumer can tell the difference between actual rape performed in front of a camera and sex acts the porn actress has consented to.
Once again, this is often true in many commercially produced product, whether it is porn or athletic shoes or pineapples: we often do not know conditions under which these products have been produced, including the possibility that they were produced by slave labor.
There are some ways around this, although not perfect: for example, you could decide to buy only from companies that have transparent labor practices and sourcing. It might be more difficult to find suppliers of ethically produced porn, but there will be more of these if more porn consumers demand it.
In the meantime, it makes no sense to hold consumers of porn to a higher standard of ethical consumption, because that is a double standard. At most, I would urge consumers to boycott any companies that are known to have problematic labor practices, whether they produce porn, shoes, or fruits and vegetables.